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CBSE Class 10 Science Chapter 3 Metals And Non-Metals

Elements

1. Metals

Physical Properties of Metals

1.  Strong, hard to cut except Na, K.
2. Malleable, beaten into sheets.
3. Ductile, can be drawn into wires.
4.  Sonorous, produce sound when we strike them.
5. Good conductors of heat and electricity.
6. High melting and boiling points except Na, K

Read and Learn More CBSE Class 10 Science Short Answer Questions

Chemical Properties of Metals

1. React with oxygen to form oxides.
2. Metals can lose electrons to form positive ions.
3. Transition metals show variable valency
   • Example: Cu⁺,Cu²⁺, Fe²⁺, Fe³⁺…………….
4. Except few, metals react with cold water, some with hot, some with steam to form oxides or hydroxides and hydrogen gas.
5. More reactive metals can displace less reactive metals from their salt solution.
6. Metals react with dilute acids to form salt and hydrogen gas except with dil. HNO₃ . They are good which is an oxidising agent.

Exceptional Properties

1. Iron is malleable and strong. It easily rusts in moist air.
2.  Iron is magnetic, and melts at 1530°C.
3. Sodium is so soft, can be cut by a knife. It floats on water, catches fire in the presence of water, and melts at 98°C.
4. Gold is unreactive, highly malleable and ductile and looks attractive.
5. Gold is used in jewellery, and melts at 1064°C.

Mg and Mn react with 5% HNO₃ to produce Hz gas.

6. Al₂O₃. BeO and ZnO are amphoteric (acidic as well as basic) oxides.

7. NO, N₂O, CO or neutral oxides.

2. Metalloids

Composition of Earth’s crust

Most of the metals occur as their compounds except gold, silver, and platinum which occur in free-state

3. Non-metals

Physical Properties of Non-Metals

1. They are brittle.
2. They exist as solids, liquids and gases.
3. They are non-lustrous except for diamond and iodine.
4. They are not conductors of heat and electricity except graphite.
5. Low melting and boiling points except for diamond and graphite.
6. Low density

Chemical Properties of Non-Metals

1. They form acidic oxides.
2.  They gain electrons to form negative ions
3. They are a good oxidising agent. oxidising agents
4. Their oxide dissolves in water forming acids
5. They do not react with dilute acids because they can’t lose electrons
6. More reactive non-metals can displace less reactive non-metals from their salt solution.

CBSE Class 10 Science Chapter 3 Metals And Non-Metals Definitions

1. Metals: Metals are the element which can easily form positive ions by ionising electrons.

For example: Sodium, Potassium, Magnesium, Iron, Copper, etc.

2. Physical characteristics of metals:

1. Conductors of heat and electricity
2. Metals have shining surface
3. Metals have a high tensile strength
4. Metals have sonority

3. Sonority: It is the characteristic ofa metal to emit a deep resonant sound when struck.

4. Tensile strength: It is the resistance of a wire to pull action and is measured by the breaking stress in kilogram per square millimetre.

5. Reactivity of metals: The electropositive character of a metal determines its reactivity.

6. Metallichydrides: The compounds of metals with hydrogen are calledmetallichydrides.

These are usually obtained by passing hydrogen over heated metals.

7. Amphoteric oxides: Such oxides which react with both acids and bases to give salt and water are called amphoteric oxides. For example: A1203, ZnO.

8. Non-metals: Non-metals are the elements which form negative ions by gaining electrons.

9. Physical characteristics of non-metals:

1. Non-metals are brittle.
2. Non-metals are non-ductile.
3. Non-metals have comparatively low melting and boiling points.
4. Non-metals have low densities.

10. Minerals: The metals found in nature in a combined state are called minerals.

11. Ore: An ore is defined as a mineral from which a metal can be extracted economically.

12. Metallurgy: The extraction of a metal from a suitable ore and its refining for use is called metallurgy or metallurgical operations.

13. Calcination: It is the process of heating the concentrated ore in the absence of air

⇒ \(\underset{\text { Zinc carbonate }}{\mathrm{ZnCO}_3(s)} \longrightarrow \underset{\text { Zinc oxide }}{\mathrm{ZnO}(s)}+\underset{\text { Carbon dioxide }}{\mathrm{CO}_2(\mathrm{~g})}\)

14. Roasting: It is the process of heating the ore in the presence of air

⇒ \(2 \mathrm{ZnS}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{ZnO}+2 \mathrm{SO}_2\)

15. Slag: Some substances when heated with the ore combine with the earthy impurities and form an easily fusible mass. The easily fusible mass is called slag.

16. Gangue:

Ores are associated with earthy or rocky materials as impurities. These impurities are called gangue or matrix.

17. Smelting:

The roasted or calcined ore is mixed with coke and heated in a furnace to obtain free metal. The process of reducing the oxide with coke is called smelting.

18. Electrolysis:

Electrolysis is the process of conduction of electricity through molten or dissolved chemicals to decompose its components.

19. Corrosion: When the surface or metal is attacked by air, water and some other substance, it is said to corrode. The phenomenon is known as corrosion.

20. Galvanisation: The coating of iron with zinc is called galvanisation.

21. Anodising: It is the process of the formation of a thick layer of metal oxide over a metallic object.

22. Alloy: An alloy is a homogeneous mixture of two or more than two metals, which have nearly the same atomic size.

23. Amalgam: It is an alloy of metal with mercury.

24. Aqua regia: The mixture of cones. HCl and cone. HNO in the ratio 3:1.

25. Important chemical reactions of metals

Reaction with oxygen:

Metal + Oxygen Metal oxide

4 Na +O₂ → 2Na₂ O(s)

4K+ O₂ → 2K₂O(s)

2Cu +O₂→ (heat) 2CuO(s)

4Al +3O₂→(heat) 2AlO(s)

2 Zn +3O₂→(heat) →2 ZnO(s)

4 Fe +3O→(heat)→2 Fe₂O₃(s)

2 Mg +O₂ → (heat) 2MgO(s)

2 Ca +O₂ →(heat)→ 2CaO(s)

Reaction with water

Metal + Water Metal Oxide + Hydrogen or hydroxide

2Na + 2H₂O→(cold)→ 2NaOH + H₂

2K + 2H₂O→(cold) →2KOH + H₂

Ca + 2H₂O→(cold)→ Ca(OH)₂ + H₂

Mg + 2H₂O→(hot)→ Mg(OH)₂ + H₂

2Al + 3H₂O→(steam)→Al₂O₃ + 3H₂

3Fe + 4H₂O→(steam)→ Fe₃O₄ + H₂

Reaction with dil acid

Metal + dil acid→ Salt + Hydrogen

Zn + 2HCl(dil)→ Salt + Hydrogen

Mg + H₂SO₄(dil)→ MgSO₄ + H₂

Mg + 2HNO₃→(5%) →Mg(NO₃)₂ + H₂

Mn + 2HNO₃→ (5%)→ Mn(NO₃)₂ + H₂

2Al + 6HCl → 2AlCl₃ + 3H₂

The metal reacts with salts

More reactive metal + salt → Salt + Less reactive metal

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Mg(s)+FeSO(aq) → MgSO₄(aq) + Fe(s)

Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)

2Al(s) + 3CuSO₄(aq) → Al₂(SO₄)₃(aq) + 3Cu

Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)

Cu +2Ag NO₃(aq)→ Ag +Cu(NO₃)₂

Ag + Cy (NO₃)₂ → No reaction

Metal oxide reaction with water

Metal oxide + water Metal hydroxide

K₂O+H₂O →2KOH

CaO+H₂O→Ca(OH)₂

MgO+H₂O→Mg(OH)

NaO +HO → 2NaOH

Metal oxide reacts with acid

Metallic oxide + Acids → Salt + Water

Salt + Water MgCl +However

ZnO + 2HCl(dil) → ZnCl₂ + H₂O

CuO + H₂SO₄(dil) →CuSO₄ + H₂O

FeO + H₂SO₄(dil)→ FeSO₄ + H₂O

Al₂O₃ + 6HCl→ Al₂Cl₂ + 3H₂O

26. Important chemical properties of metals

Reaction with oxygen

Non-metals + Oxygen Non-metal oxide (acidic oxide)

S + O₂  → SO₂ 

c + O₂  →CO₂ 

4P + 5O₂  → 2P₂O₆, NO, CO and NO are neutral oxides

4B +3O₂ → BO

Si +O₂  →  SiO₂ 

Non-metallic oxides react with water

Non-metallic oxide + water→ Acids

CO₂  + H₂O H₂CO₃ (Carbonic acid)

SO₂ + H₂O→ H₂CO₃ (Carbonic acid)

SO₃ + H₂O→ H₂SO₄ (Sulphuric acid)

P₂O₅ + 3H₂O→ 2H₃PO₄ (Phosphoric acid)

B₂O₃+ 3H₂O → 2H₃PO₄ (Phosphoric acid)

SiO₂ + H₂O → H₂SiO₃ (Silicic acid)

H₂SiO₃(Silicic acid)

Acidic oxides + Base Salt + Water

CO₂ + 2NaOH → Na₂CO₃+H₂O

CO₂ + Ca(OH)₂ → Na₂CO₃+H₂O

SO₂ + 2NaOH → Na₂SO₃ + H₂O

More reactive non-metals react with salt

More reactive non-metal + Salt → Salt+ Less reactive non-metal

More reactive non-metal + Salt

Cl₂ + 2KBr→ 2KCl + Br₂

Cl₂ + 2KI → Cl₂+ 2KI

Br₂ + 2KI →2KBr + I₂

Order of reactivity: Cl₂ > Br₂ > I₂

Order of reactivity: Cl₂ > Br₂ > I₂

Extraction of metals from ores

Alloys:

Homogeneous mixture of two or more metals which have better properties than metals. One of them can be non-metal also. Steel is an alloy of iron and carbon. It does not get rusted.

Important Alloys:

1. Stainless steel: It is an alloy of Fe. C. nickel and chromium which is hard, malleable and does not rust, It is used for utensils and surgical instruments.

2. Brass: It is an alloy of copper and zinc. It is used to make decorative articles

3. Bronze: It is an alloy of copper and tin. It’s used for medals and statues.

4. Solder is an alloy of an alloy of It is used for soldering purpose

5. Duralumin: Duralumin is an alloy of Alandmagnesium.It is used to make the body of the aeroplane

6. 24-carat gold is pure gold. It is very soft. It is alloyed with copper and silver to make it hard to make jewellery of 22-carat gold=\(\frac{22}{24} \times 100\)

= 91.6% pure

7. Al is used for transmission wires, cooking foil, drink cans, and coating CDs and DVDs. Aluminium powder is used In silver paints. Al is used as a reducing agent. Al Is used for making utensils and pressure cooker

Relative Reactivities of Metals

CBSE Class 10 Science Chapter 3 Metals And Non-Metals Short Question And Answers

Question 1. Give an example of a metal which

1. Is a liquid at room temperature.
2. Can be easily cut with a knife.
3. Is the best conductor of heat.
4. Is a poor conductor of heat.

Answer:

1. Mercury is a liquid at room temperature.
2. Sodium can be easily cut with a knife.
3. Silver is the best conductor of heat.
4. Lead is a poor conductor of heat.

Question 2. Explain the meanings of malleable and ductile.
Answer:

When a metal can be beaten into thin sheets with a hammer, the metal is called malleable and the property is called malleability. When a metal can be drawn into thin wires, the metal is called ductile and the property is called ductility.

Question 3. Write equations for the reactions of

1. Iron with steam
2. Calcium and potassium in water

Answer:

1. \(\underset{\text { Iron }}{3 \mathrm{Fe}(s)}+\underset{\text { Water }}{4 \mathrm{H}_2 \mathrm{O}(l)} \longrightarrow \underset{\text { oxide of iron }}{\mathrm{Fe}_3 \mathrm{O}_4(s)}+\underset{\text { Hydrogen }}{4 \mathrm{H}_2(g)}\)

2.

Question 4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄
Answer:

Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.

Reaction of iron with dilute sulphuric acid

⇒ \(\underset{\text { Iron }}{\mathrm{Fe}}+\underset{\text { Sulphuric acid }}{\mathrm{H}_2 \mathrm{SO}_4(\alpha q)} \longrightarrow \underset{\text { Ferrous sulphate }}{\mathrm{FeSO}_4(\alpha q)}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}}\)

Question 5. What would you observe when zinc is added to a solution of iron (2) sulphate? Write the chemical reaction that takes place.
Answer:

Zinc is more reactive than iron. When zinc is added to a solution of iron (2) sulphate, the green colour of iron (2) sulphate fades out and iron metal is deposited.

Zn(s)(zinc) + FeSO₄(aq)(Iron sulphate) → Fe(Iron)] +ZnSO(aq)(Zinc sulphate)

Question 6. Why do ionic compounds have high melting points?
Answer:

Ionic compounds do not exist as single molecules but exist as aggregates of a large number of positive and negative ions due to strong electrostatic forces. Thus, a large amount of energy is required to break the inter-ionic attraction, hence these have high melting points

Question 7. What are alloys?
Answer:

An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal. It is prepared by first melting the main metal, and then dissolving the required amount of other metals or non-metals. The mixture is then cooled to room temperature to form an alloy of a given composition.

Question 8. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer:

Those oxides which react with both acids as well as bases to produce salt and water are known as amphoteric oxides. Two examples of amphoteric oxides are Aluminium oxide (Al₂O₃) and zinc oxide (ZnO).

Question 9. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer:

In electrolytic refining of a metal M, the impure metal M is made the anode and a thin strip of pure metal M is made the cathode. A solution of the metal M salt is used as an electrolyte.

For Example:

For refining copper metal, the strip of the pure metal would be made cathode, and that of impure metal would be made anode and the electrolyte would be copper sulphate solution.

Question 10. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer:

When the copper vessel is kept in moist air, it reacts with moist carbon dioxide in the air to form a green substance. The green substance is copper carbonate, which is basic. When it is treated with lemon or tamarind juice containing acid, neutralisation of the base occurs which cleans the vessel.

Question 11. Name two metals which are purified by electrolytic refining. Mention the anode, cathode and the electrolyte used in the refining process. At which electrode would the pure metal be deposited?
Answer: 

Copper, zinc.

Impure metal is made of anode and a thin strip of pure metal is made of cathode. A solution of the metal salt is used as an electrolyte. Pure metal from the electrolyte is deposited on the cathode.

Question 12. Write the electron dot structure for sodium and chlorine atoms. How do these form a chemical bond? Name the type of bond so formed. Why does a compound so formed have a high melting point?
Answer:

The electron dot diagrams of Na and Cl are as follows:

• They form bonds by the transfer of an electron. Na loses one electron to form Na⁺ ion whereas Cl gains one electron to form Cl^– ion.
• The bond formed is an ionic or electrovalent bond.
• The compound (NaCl) thus formed has a high melting point due to the strong force of attraction between Na⁺ and Cl^– ion.

Question 13. Mention the names of the metals for the following

1. Two metals are alloyed with iron to make stainless steel.
2. Two metals are used to make jewellery.

Answer:

1. Nickel and chromium
2. Gold and platinum

Question 14. Write one example of each of

1. A metal which is so soft that, it can be cut with a knife and a non-metal which is the hardest substance.
2. A metal and a non-metal exist as a liquid at room temperature.

Answer:

1. Sodium, carbon (diamond)
2. Mercury is a liquid metal, bromine is a liquid non-metal.

Question 15. A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. State the chemical name of the black and green coating. How are they formed?
Answer:

Black coating: Silver sulphide (Ag₂S)

Green coating: Basic copper carbonate [CuCO₃.Cu(OH)₂]

The action of

1. HS or sulphur compounds are present in the atmosphere.
2. Carbon dioxide, oxygen and water vapour are present in the atmosphere.

Question 16.

1. Write the electron dot structures for potassium and chlorine.
2. Show the formation of KCl by the transfer of electrons.
3. Name the ions present in this compound, KCl.

Answer:

3. KCl has K⁺ and Cl^–.

Question 17. Explain the formation of the ionic compound CaO with an electron dot structure. An atomic number of calcium and oxygen are 20 and 8 respectively.

Name the constituent metals of bronze.

Answer:

⇒ \(\underset{2,8,8,2}{\mathrm{Ca}} \longrightarrow \mathrm{Ca}^{2+}+\underset{2,8,8}{2 \mathrm{e}^{-}}\)

⇒ \(\underset{2,6}{\mathrm{O}}+2 \mathrm{e}^{-} \longrightarrow \underset{2,8}{\mathrm{O}^{2-}}\)

Bronze is made up of copper and tin.

Question 18. Out of the two metals P and Q, P is less reactive than Q. Suggest an activity to arrange these metals in the order of their decreasing reactivity. Support your answer with a suitable chemical equation.
Answer:

Activity: In a test tube, a small amount of salt solution of P is taken and metal Q is added to it. Q being more reactive, displaces metal P from its salt solution.

Chemical equation:

Metal Q + Salt solution of P → Salt solution of Q + Metal P.

Question 19. Define an alloy. How is an alloy prepared?
Answer:

A homogeneous mixture of two or more metals or a metal and a non-metal is known as an alloy. It is prepared by first melting the primary metal, and then, dissolving the other elements in it in definite proportions.

Question 20. A compound ‘Z’ is formed by the transfer of electrons from a metal ‘X’ to a non-metal Y. Identify the type of bond formed in the compound. List three general properties of the compounds formed by such types of bonds.
Answer:

Ionic compounds are formed in these compounds.

The general properties of ionic compounds are:

1. Solid
2. High melting and boiling point
3. Soluble in water
4. Good conductor of electricity

Question 21. Give reasons for the following:

1. School bells are made up of metals.
2. Electrical wires are made up of copper.

Answer:

Because metals are sonorous.

Copper is a very good conductor of electricity.

Question 22.

1. Name a metal which does not stick to glass.
2. Name the metal which is commonly used in thermite welding.
3. What is the nature of zinc oxide?

Answer:

1. Hg (Mercury)
2. Al (Aluminium)
3. Basic

Question 23. Describe ionic compounds based on the following properties:

1. A strong force of attraction between positive and negative ions
2. Solubility of compounds in water
3. Electrical conductivity

Answer:

Owing to the strong force of attraction between the positive and negative ions, ionic compounds are solids.

• These compounds are generally brittle and break into pieces when pressure is applied.
• Ionic compounds are generally soluble in water.
• Ionic compounds in the solid state do not conduct electricity but in aqueous and molten states, they do conduct electricity.

Question 24.

1. ‘Sodium is a highly reactive metal and it cannot be obtained from its oxide by heating with carbon’. Give reason.
2. How can sodium be obtained from sodium chloride?

Answer:

Sodium cannot be obtained from its oxide by heating with carbon because carbon cannot reduce the oxides of sodium.

Sodium can be obtained from sodium chloride by the process of electrolytic reduction.

Question 25. Define the term ‘anode mud. Name the electrode made of pure metal. State the reactions taking place at the cathode and at the anode during the electrolytic refining of copper.
Answer:

The insoluble impurities which settle down at the bottom of the anode are known as anode mud.

The cathode is made of pure metal.

At anode: \(\mathrm{Cu}(s) \longrightarrow \mathrm{Cu}^{2+}(a q)+2 e^{-}\)

At cathode: \(\mathrm{Cu}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Cu}(s)\)

Question 26. Name the following:

1. A metal, which is preserved in kerosene.
2. A lustrous coloured non-metal.
3. A metal, which can melt while kept on the palm.
4. A metal, which is a poor conductor of heat.

Answer:

1. Sodium is preserved in kerosene.
2. Iodine is a lustrous coloured non-metal.
3. Gallium or caesium
4. Lead or mercury

Question 27. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer:

It is because of the following reasons:

1. Copper does not react with hot water or steam, whereas steel reacts with steam.
2. Copper is one of the best conductors of heat as compared to steel.
3. Copper has a high melting point as compared to steel.

Question 28. Write chemical equations that show aluminium oxide reacts with acid as well as base.
Answer:

⇒ \(\mathrm{Al}_2 \mathrm{O}_3+6 \mathrm{HCl} \longrightarrow 2 \mathrm{AlCl}_3+3 \mathrm{H}_2 \mathrm{O}\)

⇒  \(\mathrm{Al}_2 \mathrm{O}_3+2 \mathrm{NaOH} \longrightarrow 2 \mathrm{NaAlO}_2+\mathrm{H}_2 \mathrm{O}\)

Question 29. Explain why calcium metal after reacting with water starts floating on its surface. Write the chemical equation for the reaction. Name one more metal that starts floating after some time when immersed in water.
Answer:

Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.

⇒  \(\mathrm{Ca}(\mathrm{s})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \longrightarrow \mathrm{Ca}(\mathrm{OH})_2+\mathrm{H}_2(\mathrm{~g})\)

Magnesium reacts with hot water and starts floating due to the bubbles of hydrogen gas sticking to its surface.

Question 30. Why is it that non-metals do not displace hydrogen from dilute acids?
Answer: Those oxides which are both acidic as well as basic are called amphoteric oxides

Example: Al₂O₃, ZnO.

This is because non-metals do not supply electrons to change H+ ions into hydrogen gas.

Question 31. During the extraction of metals, electrolytic refining is used to obtain pure metals.

1. Which material will be used as anode and cathode for refining silver metal by this process?
2. Suggest a suitable electrolyte also.
3. In this electrolytic cell, where do we get pure silver after passing an electric current?

Answer:

1. Anode : Impure silver

Cathode: Pure silver

2. Electrolyte: Silver salt, such as AgNO3, AgCl, etc.

3. We get pure silver at the cathode

Question 32. Compound X and aluminium are used to join railway tracks.

1. Identify the compound X
2. Name the reaction
3. Write down its reaction.

Answer:

Compound X must be iron (3) oxide, Fe₂O₃

The reaction is known as the ‘thermite reaction’ or ‘alumino thermy’.

The reaction is carried out by igniting the mixture with a Mg-ribbon.

Question 33. When a metal X is treated with cold water, it gives a basic salt Y with the molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y, and Z and also write the reaction involved.
Answer:

The base with molecular mass 40 is NaOH.

Hence, the metal X be sodium (Na). It reacts with H₂O to form the base NaOH and liberates H₂ gas which easily catches fire

Question 34. A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.
Answer: 

Non-metal ‘X’ must be carbon. It exists in two forms, diamond and graphite.

Diamond is the hardest natural substance. Hence, ‘Y’ is a diamond.

Graphite is a good conductor of electricity. Hence, ‘Z’ is graphite.

Question 35. The following reaction takes place when aluminium powder is heated with MnO₂

⇒ \(3 \mathrm{MnO}_2(s)+4 \mathrm{Al}(s) \longrightarrow 3 \mathrm{Mn}(l)+2 \mathrm{Al}_2 \mathrm{O}_3(l)+\text { Heat }\)

1. Is aluminium getting reduced?
2. Is MnO₂ getting oxidised?

Answer:

1. No, because oxygen is added to aluminium, so it is getting oxidised
2. No, since manganese has lost oxygen, therefore it is getting reduced.

Question 36. A metal A, which is used in the thermite process, when heated with oxygen gives an oxide B, which is amphoteric. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.
Answer:

A = Aluminium

B = Al₂O₃

Question 37. A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.
Answer:

The metal that exists as a liquid at room temperature is mercury (Hg). It is obtained by heating its sulphide ore, HgS, called ‘cinnabar’ in the presence of air (roasting). The metal sulphide is first converted into metal oxide (HgO) which on further heating is reduced to Hg.

Question 38. Give the formulae of the stable binary compounds that would be formed by the combination of the following pairs of elements.

1. Mg and N₂
2. Li and O₂
3. Al and Cl₂
4. K and O₂

Answer:

1. Mg₃N₂
2. Li₂O
3. AlCl₂
4. K₂O

Question 39. A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming.

1. Identity A, B, and C
2. To which Group of the Periodic Table does A belong?

Answer:

1. A carbon, B = carbon monoxide (CO) C = Carbon dioxide (CO₂)
2. Carbon (A) belongs to group 14 of the periodic table.

Question 40. Name one metal and one non-metal that exist in a liquid state at room temperature. Also, name two metals having melting point less than 310 K (37°C).
Answer:

Metal existing in a liquid state at room temperature is mercury and non-metal is bromine.

The metals with melting points less than 310 K are caesium (Cs) and Gallium (Ga).

Question 41. Using the electronic configurations, explain how the magnesium atom combines with the oxygen atom to form magnesium oxide by transfer of electrons.
Answer:

The atomic number of magnesium

⇒ \(\underset{2,8,2}{\mathrm{Mg}} \longrightarrow \underset{2,8}{\mathrm{Mg}^{2+}+2 \mathrm{e}^{-}}\)

The atomic number of oxygen = 8

⇒  \(\underset{2,6}{\mathrm{O}}+2 \mathrm{e}^{-} \longrightarrow \underset{2,8}{\mathrm{O}^{2-}}\)

Question 42. List three properties of sodium in which it differs from the general physical properties of
most metals.
Answer:

It has low density.

It has a low melting point.

Sodium is so soft that it can be cut with a knife.

Question 43. What happens when

1. ZnCO₃ is heated in the absence of oxygen.
2. A mixture of Cu₂O and CuS is heated.

Answer:

Question 44. An element A reacts with water to form compound B which is used in whitewashing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B, and C and give the reactions involved.
Answer:

A = Ca; B = Ca (OH)₂ ; C = CaO

Question 45. A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black-coloured product. Identify M and black coloured product and also explain the reaction of M with oxygen.
Answer:

Cu + HCl/H₂SO₄/HNO₃→ No H₂ is evolved

2 Cu(s)+O₂(g)→  (Heat) →  2CuO(s) Copper(2)oxide (Black product)

Question 46. A solution of CuSO₄ was kept in an iron pot. After a few days, the iron pot was found to have several holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.
Answer:

Fe is more reactive than Cu and hence displaces Cu from CuSO, solution. The following reaction takes place:

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Question 47. Of the three metals X, Y, and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y, and Z and also arrange them in order of increasing reactivity.
Answer:

X = Na or K, Y = Mg, Z = Fe.

Increasing reactivity: Na/K > Mg > Fe.

Question 48. Element A burns with a golden flame in the air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C, and D. Also write down the equations for the reactions involved.
Answer:

A Sodium, B = chlorine and, C = Sodium chloride

2 Na(s) + Cl₂(g) → 2NaCl(s)

D = Sodium hydroxide

2 Na⁺Cl^–(aq) +2H₂O(l) →  (Electrolysis) → 2NaOH(aq)+Cl₂(g) +H₂(g)

Question 49. Two ores A and B were taken. On heating ore A gives CO, whereas, ore B gives SO What steps will you take to convert them into metals?
Answer:

Since ore A gives CO₂, and ore B gives SO₂. Therefore, ores are MCO and MS.

A can be obtained

MCO₃ →  MO+CO₂

MO+C  → M+ CO

Question 50. What happens when

1. ZnCO₃ is heated in the absence of oxygen.
2. A mixture of Cu₂O and Cu₂S is heated.

Answer:

ZnCO₃→ ZnO+CO₂↑

2Cu₂O+Cu₂S→6Cu+SO₂↑

Question 51. When a metal X is treated with cold water, it gives a basic Y with the molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
Answer:

X Sodium, Y = NaOH, Z = H₂ ↑

2 Na + 2H₂O → 2NaOH (aq) + H₂(↑)

Question 52. Give the formulae of the stable binary compounds that would be formed by the combination of the following pairs of elements.
Answer:

1. Mg, N₂
2. LiO₂
3. AlCl₃
4. K₂O

Question 53. A metal ‘E’ is stored under kerosene oil. When a small piece of it is left open in the air, it catches fire. When the product formed is dissolved in water it turns red litmus blue.

Name the metal E.

Write the chemical equation for the reaction when it is exposed to air and when the product is dissolved in water.

CBSE Class 10 Science Chapter 3 Metals And Non-Metals Multiple Choice Questions

Question 1. Which of the following properties is generally not shown by metals?

1. Electrical conduction
2. Sonorous in nature
3. Dullness
4. Ductility

Answer: 3. Dullness

Question 2. The ability of metals to be drawn into thin wire is known as

1. Ductility
2. Malleability
3. Sonorosity
4. Conductivity

Answer: 1.  Malleability

Question 3. Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same?

1. Good thermal conductivity

2. Good electrical conductivity

3. Ductility

4. High melting point

1. 1 and 2
2. 1 and 3
3. 2 and 3
4. 1 and 4

Answer: 4.  1 and 4

Question 4. Which one of the following metals does not react with cold as well as hot water?

1. Na
2. Ca
3. Mg
4. Fe

Answer: 4.  Fe

Question 5. Which of the following oxide(s) of iron would be obtained on the prolonged reaction of iron with steam?

1. FeO
2. Fe₂O₃
3. Fe₃O₄
4. Fe₂O₃ and Fe₂O₄

Answer: 3.  Fe₃O₄

Question 6. What happens when calcium is treated with water?

1. It does not react with water

2. It reacts violently with water

3. It reacts less violently with water

4. Bubbles of hydrogen gas formed stick to the surface of calcium

1. 1 and 4
2. 2 and 3
3. 1 and 2
4. 3 and 4

Answer: 4.  3 and 4

Question 7. Generally, metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)?

1. H₂SO₄
2. HCl
3. HNO₃
4. All of these

Answer: 3. HNO₃

Question 8. The composition of aqua-regia is

1. \(\begin{array}{cll}
\text { Dil. } \mathrm{HCl} & : & \text { Conc. } \mathrm{HNO}_3 \\
3 & : & 1
\end{array}\)

2. \(\begin{array}{cll}
\text { Conc. } \mathrm{HCl} & : & \text { Dil. } \mathrm{HNO}_3 \\
3  : & 1
\end{array}\)

3. Conc.HCl (3): Conc.HNO₃(1)

4. \(\begin{array}{cll}
\text { Dil. } \mathrm{HCl} & : & \text { Conc. } \mathrm{HNO}_3 \\
3 & : & 1
\end{array}\)

Answer: 3. Conc.HCl (3): Conc.HNO₃(1)

Question 9. Which of the following are not ionic compounds?

1. KCl

2. HCl

3. CCl₄

4. NaCl

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1 and 3

Answer: 2. HCl

Question 10. Which one of the following properties is not generally exhibited by ionic compounds?

1. Solubility in water
2. Electrical conductivity in solid state
3. High melting and boiling points
4. Electrical conductivity in molten state

Answer:  2. Electrical conductivity in solid state

Question 11. Which of the following metals exists in their native state in nature?

1. Cu

2. Au

3. Zn

4. Ag

1. 1 and 2
2. 1 and 3
3. 2 and 4
4. 3 and 4

Answer: 3. Zn

Question 12. Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?

1. Au

2. Cu

3. Na

4. K

1. 1 and 2
2. 1 and 3
3. 2 and 3
4. 3 and 4

Answer: 1. Au

Question 13. Silver articles become black on prolonged exposure to air. This is due to the formation of

1. Ag₃N
2. Ag₂O
3. Ag₂S
4. Ag₂S and Ag₂N

Answer: 3. Ag₂S

Question 14. Galvanisation is a method of protecting iron from rusting by coating with a thin layer of

1. Galium
2. Aluminium
3. Zinc
4. Silver

Answer: 3. Galium

Question 15. Stainless steel is a very useful material for our life. In stainless steel, iron is mixed with

1. Ni and Cr
2. Cu and Cr
3. Ni and Cu
4. Cu and Au

Answer: 1. Ni and Cr

Question 16. If copper is kept open in the air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of

1. CuSO₄
2. CuCO₃
3. Cu(NO₃)₂
4. CuO

Answer: 2.  CuCO₃

Question 17. Generally, metals are solid. Which one of the following metals is found in a liquid state at room temperature?

1. Na
2. Fe
3. Cr
4. Hg

Answer:  4. Hg

Question 18. Which of the following metals are obtained by electrolysis of their chlorides in a molten state?

1. Na

2. Ca

3. Fe

4. Cu

1. 1 and 4
2. 3 and 4
3. 1 and 3
4. 1 and 2

Answer: 4. 1 and 2

Question 19. Generally, non-metals are not lustrous. Which of the following non-metal is lustrous?

1. Sulphur
2. Oxygen
3. Nitrogen
4. Iodine

Answer: 4. Iodine

Question 20. Which one of the following four metals would be displaced from the solution of its salts by the other three metals?

1. Mg
2. Ag
3. Zn
4. Cu

Answer: 2. Ag

Question 21. 2 ml each of concentrated HCL, HNO, and a mixture of concentrated HCl and concentrated HNO, in the ratio of 3: 1 were taken in test tubes labelled as A, B, and C.  A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be

1. Al
2. Au
3. Cu
4. Pt

Answer: 2. Au

Question 22. An alloy is

1. An element
2. A compound
3. A homogeneous mixture
4. A heterogeneous mixture

Answer: 3. A homogeneous mixture

Question 23. An electrolytic cell consists of

1. Positively charged cathode

2. Negatively charged anode

3. Positively charged anode

4. Negatively charged anode

1. 1 and 2
2. 3 and 4
3. 1 and 3
4. 2 and 4

Answer:  2. 3 and 4

Question 24. During electrolytic refining of zinc, it gets

1. Deposited on cathode
2. Deposited on anode
3. Deposited on the cathode as well as anode
4. Remains in the solution

Answer: 1. Deposited on cathode

Question 25. An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following

1. Mg
2. Na
3. P
4. Ca

Answer: 2.  Na

Question 26. Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contain non-metal as one of its constituents?

1. Brass
2. Bronze
3. Amalgam
4. Steel

Answer: 4.  Steel

Question 27. Which among the following statements is incorrect for magnesium metal?

1. It burns in oxygen with a dazzling white flame
2. It reacts with cold water to form magnesium oxide and evolves into hydrogen gas
3. It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas
4. It reacts with steam to form magnesium hydroxide and evolves hydrogen gas

Answer: 2. It reacts with cold water to form magnesium oxide and evolves into hydrogen gas

Question 28. Which among the following alloys contain mercury as one of its constituents?

1. Stainless steel
2. Alnico
3. Solder
4. Zinc amalgam

Answer: 4.  Zinc amalgam

Question 29. The reaction between X and Y, forms compound Z. X loses electrons and Y gains electrons. Which of the following properties is not shown by Z?

1. Has a high melting point
2. Has a low melting point
3. Conducts electricity in a molten state
4. Occurs as solid

Answer: 2. Has a low melting point

Question 30. The electronic configurations of three elements X, Y, and Z are X-2, 8; Y – 2, 8, 7 and Z-2, 8, 2. Which of the following is correct?

1. X is a metal
2. Y is a metal
3. Z is a non-metal
4. Y is a non-metal and Z is a metal

Answer: 4. Y is a non-metal and Z is a metal

Question 31. Although metals form basic oxides, which of the following metals form an amphoteric oxide?

1. Na
2. Ca
3. Al
4. Cu

Answer: 3. Al

Question 32. Generally, non-metals are not conductors of electricity. Which of the following is a good conductor of electricity?

1. Diamond
2. Graphite
3. Sulphur
4. Fullerene

Answer: 2. Graphite

Question 33. Electrical wires have a coating of an insulating material. The material generally used is

1. Sulphur
2. Graphite
3. PVC
4. All can be used

Answer: 3. PVC

Question 34. Which of the following non-metals is a liquid?

1. Carbon
2. Bromine
3. Phosphorus
4. Sulphur

Answer: 2. Bromine

Question 35. Which of the following can undergo a chemical reaction?

1. MgSO₄ + Fe
2. ZnSO₄+ Fe
3. MgSO₄ + Pb
4. CuSO₄+ Fe

Answer: 4.  CuSO₄+ Fe

Question 36. Which one of the following figures correctly describes the process of electrolytic refining?

Answer: 3.

Question 37. Which of the following pairs will give displacement reactions?

1. NaCl solution and copper metal
2. MgCl₂, solution and aluminium metal
3. FeSO₄ solution and silver metal
4. AgNO₃, solution and copper metal

Answer: 4. AgNO₃, solution and copper metal

Question 38. Which of the following methods is suitable for preventing an iron frying pan from rusting?

1. Applying grease
2. Applying paint
3. Applying a coating of zinc
4. All of the above

Answer:  4.  All of the above

Question 39. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

1. Calcium
2. Carbon
3. Silicon
4. Iron

Answer: 1. Calcium

Question 40. Food cans are coated with tin and not with zinc because

1. Zinc is costlier than tin.
2. Zinc has a higher melting point than tin.
3. Zinc is more reactive than tin.
4. Zinc is less reactive than tin.

Answer: 3. Zinc is more reactive than tin.

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts

Salts:

Indicators:

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Definitions

1. Acids: Acids are sour and change the colour of blue litmus to red.

Examples of Acids:

Hydrochloric acid: HCI

Sulphuric acid: H₂SO₄

Nitric acid: HNO₃

Acetic acid: CH₃COOH

Phosphoric acid: H₃PO₄

Read and Learn More CBSE Class 10 Science Short Answer Questions

2. Properties of an Acidic Solution:

1. Tastes sour.
2. Reacts with metals such as zinc, magnesium, etc. liberating hydrogen gas.
3. Changes the colour of litmus from blue to red.
4. Conducts electricity.

3. Bases: Bases are bitter and change the colour of red litmus to blue

Examples of Bases:

Sodium hydroxide: NaOH

Potassium hydroxide: KOH

Ammonium hydroxide: NH₄OH

Calcium hydroxide : Ca(OH)₂

Barium hydroxide : Ba(OH)₂

4. Properties of a Basic Solution:

1. Tastes bitter, and feels slippery.
2. Reacts with an acidic solution to neutralize the properties or characteristics of an acid.
3. Changes the colour of litmus from red to blue.
4. Conducts electricity.

5. Indicators:

Indicators are chemical substances which give different colours in acidic or basic solutions.

6. Olfactory indicators:

The substances which have different odours in acid and base solution. For example, vanilla essence has a characteristic pleasant-smelling acid solution and no smell in an alkali solution.

7. Reaction of acids with metals:

Acid + Metal→ Salt + Hydrogen gas

H₂SO₄(aq) + Zn(s)→ ZnSO₄(aq) + H₂(g)

8. Reaction of bases with metals:

Base + Metal→ Salt + Hydrogen

2NaOH + Zn→ Na₂ZnO₂+ H₂

9. Reaction of Acids with metal Carbonates:

Acid + Metal Carbonate→ Salt + CO₂ + H₂O

2HCl(aq) + Na₂CO₃(s)→2NaCl(aq) + CO₂(g) + H₂O(Z)

10. Reaction of Acids with metal Hydrogen Carbonates:

Acid + Metal Hydrogen Carbonate→ Salt + CO₂ + H₂O

HCl(aq) + NaHCOg(s) NaCl (aq) + CO₂(aq) + H₂O(l)

11. Neutralization reaction:

When the effect of a base is nullified by an acid and vice-versa is called a neutralization reaction.

Base + acid→ Salt + water

NaOH + HCl→ NaCl + H₂O

12. Antacids:

Antacids are mild alkalies and contain sodium hydrogen carbonate. These are used for getting relief from acidity and indigestion and sometimes, even headaches.

13. Reaction of Acids with metallic Oxides:

Acid + Metal Oxides → Salt + Water

2HCl(aq) + CuO(s)

CuCl₂(aq) + H₂O(l)

14. All acids generate H⁺ ions and all bases generate OH^– ions in the presence of water and this helps acids and bases to conduct electricity.

15. Universal indicators:

An indicator which passes through a series of colour changes over a wide range of H₃O⁺ (hydronium) ion concentrations is called a universal indicator. It is a mixture of several indicators.

16. pH: pH is a number which indicates the acidic or basic nature of a solution.

17. pH scale: pH scale is the scale for measuring hydrogen ion or hydronium ion concentration in a solution.

pH =- log [H₃O⁺]

18. Acid rain: When the pH ofrain water is less than 5-6, is called acid rain.

19. Dilute acid: A dilute acid solution containing only a small amount of acid and a large amount of water.

20. Concentrated acid: A concentrated acid contains a large amount of acid and a small amount of water.

21. Salts: Salts are formed by the combination of acids and bases

Examples of Salts:

Sodium chloride: NaCl

Sodium carbonate: Na₂CO₃

Sodium hydrogen carbonate: NaHCO₃

Ammonium nitrate: NH₄NO₃

Potassium sulphate: NH₄NO₃

22. Properties of a Salt Solution:

1. Tastes salty.
2. The colour of the litmus solution usually does not change when added to a salt solution. However, some salts turn blue litmus red whereas others turn red litmus blue.
3. Conducts electricity.

23. Alkali: The hydroxide of metals which dissolve in water are known as alkalies.

24. Normal salt: It does not hydrolyse in water.

25. Acidic salt: It hydrolyses in water to give strong acids like H₂SO₄.

26. Basic salt: It hydrolyses in water to give a strong base like NaOH.

27. Water of crystallization: Water of crystallization is the fixed number of water molecules present in one formula unit of salt.

For example: CuSO₄.5H₂O, Na₂CO₃.10H₂O.

28. Deliquescence: A substance that absorbs moisture gradually from the air is called a deliquescent substance and this phenomenon is called deliquescence.

29. Carbonation: It is a process in which brine (NaCl) saturated with ammonia is allowed to come in contact with carbon dioxide under pressure to form sodium bicarbonate.

30. Antichlor: Antichlor is a substance used to remove excess chlorine from material or cloth.

For example sodium bisulphite, and sodium thiosulphate.

31. Hydrolysis: The interaction of a salt with water to give an acid and base is called salt hydrolysis.

32. Hydrated salts: Some salts crystallize with a fixed number ofwater molecules attached to one formula unit of salt.

33. Common Salt- Sodium Chloride (NaCl)

NaOH + HCl→ NaCl + H₂O

34. Caustic soda- Sodium hydroxide (NaOH)

2 NaCl(aq) +2H₂O(l) → Electricity  → 2NaOH (aq) +Cl(g)+H(g)

35. Bleaching Powder- Calcium Oxychloride (CaOCl₂)

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

36. Baking Soda- Sodium hydrogen Carbonate (NaHCO₃)

NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl

37. Washing Soda- Sodium Carbonate decahydrate  → Na₂CO₃.10H₂O

38. Plaster of Paris: CaSO₄. H₂O is known as Plaster of Paris when wetted with water sets to a hard porous mass within 10-15 minutes

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Short Question And Answers

Question 1. Five solutions A, B, C, D and E when tested with a universal indicator showed pH of 4, 1,11,7 and 9, respectively. Which solution is it?

1. Neutral
2. Strongly alkaline
3. Strongly acidic?
4. Weakly alkaline?

Arrange the pH in increasing order of hydrogen-ion concentration.
Answer:

1. D
2. C
3. B
4. A
5. E

11<9<7<4<1

Question 2. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. The amount and concentration taken for both acids are the same. In which test tube will the fizzing occur more vigorously and why?
Answer:

Fizzing will occur more vigorously in test tube A containing hydrochloric acid. This is because hydrochloric acid is stronger than acetic acid and gives more H⁺ ions quickly.

Thus, the reaction between magnesium ribbon and HCl is faster than between Mg and acetic acid.

Question 3. A milkman adds a very small amount of baking soda to fresh milk.

1. Why does he shift the pH ofthe fresh milk from 6 to slightly alkaline?
2. Why does this milk take a long time to set as curd?

Answer:

1. The milkman adds a little baking soda to fresh milk to make it slightly alkaline so that it can be preserved for a longer time.
2. Initially, lactic acid formed is used up to neutralize the base and when more lactic acid is formed, the milk sets as curd.

Question 4. Give two important uses of washing soda and baking soda.
Answer:

Uses of baking soda:

1. It is used in bakery.
2. It is used in soda acid fire extinguishers.

Uses of washing soda:

1. It is used in the manufacture of glass, soap and paper.
2. It is used for removing the permanent hardness of water

Question 5. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents ofeach test tube?
Answer:

1. Dip red litmus paper separately in three test tubes.
2. The test tube in which red litmus turns blue contains the basic solution. Now dip the blue litmus in the other two test tubes.
3. The tube which turns blue litmus red contains the acid solution. The tube in which litmus paper gives a purple colour contains distilled water.

Question 6. Why should curd and sour substances not be kept in brass and copper vessels?
Answer:

1. Curd and sour substances contain acids which react with brass and copper vessels.
2. Thus, brass and copper vessels get corroded.
3. Further, the products formed make the food unfit for eating.

Question 7. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride
Answer:

Since the end product is calcium chloride and the gas formed extinguishes a burning candle, it is CO₂ and metal compound A must be calcium carbonate. Hence, the balanced chemical equation for the reaction is as below

CaCO₃+ 2HCl→CaCl + CO₂ + H₂O

Question 8. Why do HCl, HNO₃, etc., show acidic characteristics in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic characteristics?
Answer:

Compounds like HCl, HNO₃, etc. release H⁺ ions in aqueous solution and hence show acidic character while alcohol and glucose do not release H⁺ ions in aqueous solution, and hence do not show acidic character.

Question 9. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer:

When water is added to acid, there is a sudden rise in temperature with explosion and the acid being present in bulk, it gets spilt on your body and clothes.

When an acid is added to water, the water is in bulk and the acid being heavier settles down and the heat evolved is dissipated in the water itself hence, the spurting of the liquid is minimised. For this reason, it is recommended that acid should be added to water in small amounts with stirring to dilute the concentrated acid.

Question 10. What will happen if a solution ofsodium hydrocarbonate is heated1? Give the equation of the reaction involved.
Answer:

Sodium hydrogen carbonate solution on heating gives sodium carbonate, water with evolution of carbon dioxide gas.

2 NaHCO₃(aq) → (Heat) → Na₃CO₂(s)+H₂O(l)+CO₂(g)

Question 11. Write an equation to show the reaction between Plaster of Paris and water.
Answer:

The reaction between Plaster of Paris and water:

⇒ \(\underset{\text { Plaster of Paris }}{2 \mathrm{CaSO}_4 \cdot \frac{1}{2} \mathrm{H}_2 \mathrm{O}}+\mathrm{H}_2 \mathrm{O} \longrightarrow \underset{\text { Gypsum }}{2 \mathrm{CaSO}_4 \cdot 2 \mathrm{H}_2 \mathrm{O}}\)

Question 12. Crystals of copper sulphate are heated in a test tube for some time

1. What is the colour of copper sulphate crystals

1. Before heating, and
2. After heating?

2. What is the source of liquid droplets? Seen on the inner upper side of the test tube during the heating process?

Answer:

1. 

1. Blue
2. White

2. Crystals of copper sulphate (CuSO₄.5H₂O) contain water of crystallisation and on heating these crystals lose water and become white. This lost water can be seen in the form of droplets on the inner upper side ofthe test tube.

Question 13. Effervescence arc formed when the batter for cake is heated. Which substance is present in the batter? Name the gas evolved. Write the chemical equation involved.
Answer:

The substance present is baking soda (NaHCO₃).

The gas evolved in CO

2NaHCO₃ → (Heat)→ Na₂CO₃ + H₂O + CO

Question 14. State the number of water molecules present in crystals of washing soda and Plaster of Paris. What are these water molecules called?
Answer:

1. Washing soda: 10 molecules of water.

Plaster of Paris: 1/2 molecule of water.

2. These molecules are called water of crystallisation.

Question 15. Acids do not show acidic behaviour in the absence of water but do so in water. Justify this statement with the help ofa chemical equation.
Answer:

Acids ionise in aqueous medium to form hydrogen ions. These hydrogen ions cannot exist alone, they exist after combining with water molecules. Thus, aqueous hydrogenions which are responsible for acidic behaviour can exist in the presence of water only.

H⁺(Hydrogen ion)+H₂O(water) + H₃O⁺ (Hydronium ion)

These hydrogen ions are as shown as H⁺(aq) or hydronium ions (H₂O⁺).

Question 16. Give three practical applications of a neutralisation reaction.
Answer:

• Antacids have been developed based on neutralisation reactions.
• Toothpaste is basic which neutralises the excess of acid produced in our mouth.
• Milkman adds a very small amount of baking soda to milk to neutralise the lactic acid produced in the milk.

Question 17.

1. Define olfactory indicators. Name two substances which can be used as olfactory indicators.
2. Choose strong acids from the following:
3. CH₃COOH, H₂SO₄, H₂CO₃, HNO₃

Answer:

1. Those substances whose smell (odour) changes in acidic or basic solution are called olfactory indicators,

Example: Onion and vanilla.

2. H₂SO₄ and HNO₃ are strong acids.

Question 18. 15 mL of water and 10 mL of sulphuric acid are to be mixed in a beaker.

1. State the method that should be followed with reason.
2. What is this process called?

Answer:

1. The acid is to be added slowly in water to prevent the mixture to be splashed. The reaction is highly exothermic, therefore, constant cooling should be done.
2. The process is called dilution.

Question 19. The marble statues are often slowly corroded when kept in open for a long time. Give a suitable reason.
Answer:

Chemically, marble is calcium carbonate. All metal carbonates and hydrogen carbonates react with acids to give corresponding salt, carbon dioxide and water.

Calcium carbonate reacts with acids to form calcium hydrogen carbonate, which is soluble in water and thus washed away. So the marble statues are slowly corroded.

CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)

Question 20.

1. State the purpose of developing scale.
2. Mention the pH range for acids.
3. What is the pH of acid rain and how it affects aquatic life?

Answer:

1. The purpose of developing a pH scale was to quantify the amount of H⁺ or OH^– ions in a solution.
2. The pH range for acids is 0 -7.
3. When the pH ofrain water is less than 5.6, it is called acid rain. It lowers the pH of river water. Thus, the survival of aquatic life becomes difficult.

Question 21. Deepika prepares HCl gas in her school laboratory using certain chemicals. She puts both dry and wet blue litmus papers in contact with the gas.

1. Name the reagents used by Deepika to prepare HCl gas.
2. State the colour changes observed with the dry and wet blue litmus paper.
3. Show the formation of ions when HCl gas combines with water.

Answer:

The reagents used by Deepika to prepare HCl gas are sodium chloride and sulphuric acid.

There is no colour change observed with dry litmus paper. However, wet blue litmus paper turns red.

HCI + H₂O → H₃O⁺ + Cl^–

Question 22.

1. If we take hydrochloric acid and acetic acid of the same concentration, which one will produce less H⁺ ion concentration? Out of two, which one is a weak acid?
2. If someone is suffering from acidity, which ofthe following would you suggest to cure it: Vinegar, orange juice, or baking soda solution? Give reasons for your cone.

Answer:

1.

1. Out of hydrochloric acid and acetic acid of the same concentration, acetic acid will produce fewer H⁺ ions.
2. Acetic acid is weaker than hydrochloric acid.

2. If someone is suffering from acidity,I would suggest baking soda solution to cure it because it neutralises the excess acid produced in the stomach and provides relief.

Question 23. Write the chemical name and formula of the following:

1. Salt is formed by the combination of weak acids like carbonic acid and strong bases like sodium hydroxide.
2. Basic substance formed by the chlor-alkali process.
3. Substances are added in cakes to make them fluffy.

Answer:

1. Sodium carbonate (Na₂CO₃).
2. Sodium hydroxide (NaOH).
3. Sodium hydrogen carbonate (NaHCO₃).

Question 24.

1. Name the products obtained in the chlor-alkali process.
2. Name the gases liberated at the anode and at the cathode respectively.
3. Name the solution which is used as raw material in this process.

Answer:

1. Chlorine gas, hydrogen gas and sodium hydroxide solution.
2. Chlorine gas is given off at the anode and hydrogen gas at the cathode.
3. Brine solution

Question 25. Explain why

1. The colour of copper sulphate crystals changes on heating.
2. Baking soda acts as an antacid.
3. An acid should be added to water while diluting. 

Answer:

1. It loses its 5 molecules of water of crystallisation, hence colour changes.
2. It is alkaline and neutralises excess acid to relieve pain.
3. As dilution of acids is an exothermic reaction and adding water to acids will splash and cause burns

Question 26.

1. Give the chemical names of acids present in

1. Ant
2. Lemon
3. Milk
4. Tomato

2. Write the chemical names of two salts belonging to the sodium family

Answer:

1.

1. Formic acid/methanoic acid
2. Citric acid
3. Lactic acid
4. Oxalic acid

2.

1. Soddiumcarbonate (Na₂CO₃)
2. Sodium sulphate (Na₂SO₄)

Question 27.

1. What do you understand by the term hydrated salt?
2. Give two examples of hydrated salt which are white and state their chemical formula.

Answer:

1. The salts having water of crystallisation with them are known as hydrated salts. Some salts unite with a definite quantity of water while crystallising out from their solutions, and this is known as the water of crystallisation.

2.

1. Sodium sulphate decahydrate (Na₂CO₃.10H₂O). It is commonly known as washing soda.
2. Hydrated calcium sulphate (CaSO₄.2H₂O). It is commonly known as gypsum.

Question 28. Given below are the pH values of our different liquids: 7.0, 14.0, 4.0, 2.0, Which of these could be that of

1. Lemon juice
2. Distilled water
3. 1 M sodium hydroxide solution
4. Tomato juice

Answer:

1. Lemon juice pH = 2.0

2. Distilled water pH = 7.0

3. 1 M NaOH pH = 14.0

4. Tomato juice pH = 4.0

Question 29.

1. Write the name given to bases that are highly soluble in water. Give an example.
2. How is tooth decay related to pH? How can it be prevented?
3. Why does a bee sting cause pain and irritation? Rubbing baking soda on the sting area gives relief. How?

Answer:

1. Alkali Example: NaOH (Sodium hydroxide)
2. The lower the pH, the more will be tooth decay. Acid reacts with Ca3(P04)2 and causes tooth decay. It can be prevented by brushing our teeth after every meal.
3. It is due to formic acid. Sodium hydrogen carbonate (Baking soda) neutralises formic acid giving relief.

Question 30. “Sodium hydrogen carbonate is a basic salt”. Justify the statement. How is it converted into washing soda? Explain.
Answer:

Sodium hydrogen carbonate is a salt of sodium hydroxide (strong base) and carbonic acid (weak acid).

It is a basic salt. It is converted into washing soda by heating followed by crystallisation

2 NaHCO₃ →  (Heat) → Na₂CO₃ + CO₂ +H₂O

Question 31. A white powder is added while baking bread and cakes to make them soft and fluffy. Write the name of the powder. Name its main ingredients. Explain the function ofeach ingredient. Write the chemical reaction taking place when the powder is heated during baking.
Answer:

Baking powder.

It consists of sodium hydrogen carbonate and tartaric acid. Sodium hydrogen carbonate gives CO₂ which makes cake soft and fluffy. Tartaric acid neutralises the bitterness due to the sodium carbonate produced.

2NaHCO₃(s)→  (Heat) → Na₂CO₃(s) +CO₂(g) +H₂O(l)

Question 32. Classify the following salts into acidic, basic and neutral: Potassium, sulphate, ammonium chloride, sodium carbonate, sodium chloride.
Answer:

Neutral: Potassium sulphate, Sodium chloride

Acidic: Ammonium chloride

Basic: Sodium carbonate

Question 33.

1. Name the compound which is obtained from baking soda and is used to
   permanent hardness of water.
2. Write its chemical formula.
3. What happens when it is recrystallised from its aqueous solution?

Answer:

1. Sodium carbonate is obtained from baking soda and is used to remove the hardness of water.
2. Na₂CO₃.
3. It changes to washing soda, Na₂CO₃.10H₂O

Question 34. Tooth enamel is one ofthe hardest substances in our body. How does it undergo damage due to eating chocolates and sweets? How does toothpaste prevent this damage?
Answer:

Tooth enamel is made up of calcium phosphate. Chocolates and sweets produce acid in our mouth which reacts with enamel (calcium phosphate) and leads to cavities. We should brush our teeth after every meal as well as after eating sweets, etc.

Question 35.

1. What is a universal indicator?
2. Write the chemical equation involved in the preparation ofsodium hydroxide. Name the process.

Answer:

1. Universal is a mixture of synthetic Indicators which is used to find pH of solutions,

2. 2NaCl(aq) + 2H₂O(Z)→  (Electrolysis)→ 2NaOH(aq)+ H₂(g) + Cl₂(g)

It is called the chlor-alkali process.

Question 36. What happens when chlorine is passed over slaked lime at 313K? Write the chemical equation of the reaction involved and state two uses ofthe product obtained.
Answer:

Bleaching powder is formed

Ca(OH)₂(s) +Cl₂(g) → (313 K) → CaOCl₂(s)+H₂O(l)

Bleaching powder Uses:

1. It is used as a bleaching agent in paper and textile industries.
2. It is used as a disinfectant in the purification of drinking water.

Question 37. Name the acid present in an ant sting andgive its chemical formula. Also, give a common method to get relief from the discomfort caused by the ant sting.
Answer:

The acid present in ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. To get relief one should apply any available basic salt

Example: Baking soda (NaHCO₃) on it.

Question 38. What happens when nitric acid is added to the shell?
Answer:

Eggshell contains CaCO₃. When nitric acid is added to it, the following reaction takes place with the evolution of CO₂

CaCO₃ + 2 HNO₃ → Ca(NO₃)₂ + H₂O + CO₂

As a result, the shell slowly dissolves in nitric acid.

Question 39. A student prepared solutions of

1. An acid and
2. A base in two separate beakers.

She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?
Answer:

If litmus paper is not available, phenolphthalein and methyl orange can be used.

Take a few drops of the two solutions in two separate test tubes. Add 1-2 drops of phenolphthalein in each of them. The solution which turns phenolphthalein pink is a base.

The other solution (acidic) will remain colourless. Clean the test tubes and repeat the experiment with methyl orange. The solution which turns methyl orange red is an acid. The colour in the other (basic) solution will be yellow.

Question 40. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for the removal of the hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B, and C. Heat
Answer:

So A = NaHCO₃

B = Na₂CO₃

C = CO₂

Question 41. What are strong and weak acids? In the following list of acids, separate strong acids from weak acids. Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.
Answer:

In aqueous solutions, strong acids ionise completely and provide hydronium ions. On the other hand, weak acids are partially ionised and an aqueous solution of the same molar concentration provides a much smaller concentration of H₃O⁺ ions.

1. Strong acids—Hydrochloric acid, sulphuric acid, nitric acid
2. Weak acids—Citric acid, acetic acid, formic acid

Question 42. When zinc metal is treated with a dilute solution ofa strong acid, a gas is evolved, which is utilisedin the hydrogenation of oil. Name the gas evolved. Write the chemical equation ofthe reaction involved and also write a test to detect the gas formed.
Answer:

When zinc reacts with a dilute solution of strong acid, it forms salt and hydrogen gas is evolved.

Zn + 2HCl→  ZnCl₂ + H₂

When a burning splinter is brought near the mouth ofthe test tube, the gas burns with a pop sound.

Question 43. Kiran was suffering from toothache. She never brushed her teeth before sleeping at night.

1. She loves to eat chocolates and ice cream.
2. What is, in general, the cause of toothache?
3. What our teeth are made up of?
4. How does toothpaste help in preventing toothache?

Answer:

1. Tooth decay starts when pH of the mouth is lower than 5.5. The acid so produced attacks the teeth and produces cavities which cause pain.
2. Calcium phosphate.
3. Toothpaste is generally basic, thus it helps in neutralising acids.

Question 44. Karan’s mother had severe pain when a honeybee stung her hand. Karan’s granny tried to relieve the pain by rubbing a metal on the stung area. But Karan picked up the baking powder from the kitchen and applied it on her mother’s hand which quickly relieved the pain.

1. Why does honeybee stinging cause pain?
2. How does baking powder relieve the bee-sting pain?
3. What value of Karan is seen in the above case?

Answer:

1. Honeybee sting consists of acid that is released in our body and causes pain.
2. Baking powder is basic, it neutralises the acid released in our body by bee-sting and relieves the pain.
3. Karan showed the value of prompt, proactive and responsible behaviour.

Question 45. Pooja’s friend is very fond, of coffee. He drinks a cup of coffee every day before he goes to school and faces the problem of stomachache very often. Pooja advised him not to drink coffee in the morning.

1. What was the cause of stomachache?
2. What would be the pH of stomach juices after consuming coffee?
3. What values of Pooja are reflected in the above act?

Answer:

1. A cup of coffee causes acidity that leads to stomachache.
2. The pH of the stomach after drinking coffee is 5.
3. Pooja showed the value of concern, caring and awareness.

Question 46. Substance A, an oxide of group 2 elements, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify A’ and also write the chemical reaction involved.
Answer:

A is calcium and chemical reaction involved:

CaO(s) + H₂O(Z) → (Basic solution)Ca(OH)₂(aq)

Question 47. What happens when the shell is placed in concentrated nitric acid in a beaker?
Answer:

Evolution of CO₂ occurs and the shell dissolves slowly

⇒ \(\mathrm{CaCO}_3+2 \mathrm{HNO}_3(\text { Conc. }) \longrightarrow \mathrm{Ca}\left(\mathrm{NO}_3\right)_2+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2(\uparrow)\)

Question 48. In one ofthe industrial processes used for the manufacture of NaOH, a gas X’ is formed as a by-product. The gas ‘X reacts with lime water to give a compound which is used as a bleaching agent in the chemical industry. Identify X’ and IT.
Answer:

X = Cl₂ and Y = CaOCl₂

⇒ \(\mathrm{Ca}(\mathrm{OH})_2+\underset{[\mathrm{X}]}{\mathrm{Cl}_2} \longrightarrow \underset{[\mathrm{Y}]}{\mathrm{CaOCl}_2}+\mathrm{H}_2 \mathrm{O}\)

CBSE Class 10 Science Chapter 2 Acids And Bases And Salts Multiple Choice Questions

Question 1. What happens when a solution of an acid is mixed with a tube?

1. The temperature ofthe solution increases

2. The temperature ofthe. solution decreases

3. The temperature ofthe solution remains the

4. Salt formation takes place

1. 1only
2. 1 and 3
3. 2 and 3
4. 1 and 4

Answer: 4.1 and 4

Question 2. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solutions would reverse the change? solution of a base in a test same

1. Baking powder
2. Lime
3. Ammonium hydroxide solution
4. Hydrochloric acid

Answer: 4. Hydrochloric acid

Question 3. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to

1. Absorb the evolved gas
2. Moisten the gas
3. Absorb moisture from the gas
4. Absorb Cl^– ions from the evolved gas

Answer: 3.  Absorb moisture from the gas

Question 4. Which ofthe following salts does not contain water of crystallisation?

1. Blue vitriol
2. Baking soda
3. Washing soda
4. Gypsum

Answer:  2. Baking soda

Question 5. Sodium carbonate is a basic salt because it is a salt of

1. Strong acid and strong base
2. Weak acid and weak base
3. Strong acid and weak base
4. Weak acid and strong base

Answer: 4. Weak acid and strong base

Question 6. Calcium phosphate is present in tooth enamel. Its nature is

1. Basic
2. Acidic
3. Neutral
4. Amphoteric

Answer: 1.  Basic

Question 7. A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of the paper to greenish-blue?

1. Lemon juice
2. Vinegar
3. Common salt
4. An antacid

Answer: 4. An antacid

Question 8. Which of the following gives the correct increasing order of acidic strength?

1. Water < Acetic acid < Hydrochloric acid
2. Water < Hydrochloric acid < Acetic acid
3. Acetic acid < Water < Hydrochloric acid
4. Hydrochloric acid < Water < Acetic acid

Answer: 1.  Water < Acetic acid < Hydrochloric acid

Question 9. If should a few be dropped of? a concentrated acid accidentally spills over the hand ofa student, what should be done?

1. Wash the hand with saline solution
2. Wash the hand immediately with plenty of water and apply a paste ofsodium hydrogen carbonate
3. After washing with plenty of water, apply a solution of sodium hydroxide to the hand
4. Neutralise the acid with a strong alkali

Answer: 2.  Wash your hand immediately with plenty of water and apply a paste ofsodium hydrogen carbonate

Question 10. Sodium hydrogen carbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?

1. It turns lime water milky

2. It extinguishes a burning splinter

3. It dissolves in a solution ofsodium hydroxide

4. It has a pungent odour

1. 1 and 2
2. 1, 2 and 3
3. 2, 3 and 4
4. 1 and 4

2.  1, 2 and 3

Question 11. Common salt besides being used in the kitchen can also be used as the raw material for making

1. Washing soda

2. Bleaching powder

3. Baking soda

4. Slaked lime

1. 1 and 3
2. 2 and 3
3. 1 and 4
4. 2 and 4

Answer: 3.  1 and 4

Question 12. One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is

1. Hydrochloric acid
2. Tartaric acid
3. A cetic acid
4. Sulphuric acid

Answer:  2. Tartaric acid

Question 13. To protect from tooth decay we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is

1. Acidic
2. Neutral
3. Basic
4. Corrosive

Answer: 3. Basic

Question 14. Which ofthe following statements is correct about an aqueous solution of an acid and of a base?

1. The higher the pH, the stronger the acid

2. The higher the pH, the weaker the acid

3. The lower the pH, the stronger the base

4. The lower the pH, the weaker the base

1. 1 and 3
2. 2 and 3
3. 1 and 4
4. 2 and 4

Answer: 4. 2 and 4

Question 15. The pH of the gastric juices released during digestion is

1. Less than 7
2. More than 7
3. Equal to 7
4. Equal to 0

Answer: 1. Less than 7

Question 16. Which ofthe following phenomena occur, when a small amount of acid is added to water?

1. Ionisation

2. Neutralisation

3. Dilution

4. Salt formation

1. 1 and 2
2. 1 and 3
3. 2 and 3
4. 2 and 4

Answer:  2. 1 and 3

Question 17. Which one ofthe following can be used as an acid-base indicator by a visually impaired student?

1. Litmus
2. Turmeric
3. Vanilla essence
4. PetuniaI leaves

Answer: 3. Vanilla essence

Question 18. Which of the following substances will not give carbon dioxide on treatment with dilute acid?

1. Marble
2. Limestone
3. Baking soda
4. Lime

Answer: 4. Lime

Question 19. Which ofthe following is acidic?

1. Lime juice
2. Human blood
3. Lime water
4. Antacid

Answer: 1.  Lime juice

Question 20. In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus was set up.

1. Which among the following statement(s) is(are) correct?

2. The bulb will not glow because the electrolyte is not acidic

3. The bulb will glow because NaOH is a strong base and furnishes ions for conduction

4. The bulb will not glow because the circuit is incomplete

The bulb will not glow because it depends upon the type of electrolytic solution

1. 1 and 3
2. 2 and 4
3. 2 only
4. 4 only

Answer: 3. 2 only

Question 21. Which ofthe following is used for the dissolution of gold?

1. Hydrochloric acid
2. Sulphuric acid
3. Nitric acid
4. Aqua regia

Answer: 4.  Aqua regia

Question 22. Which of the following is not a mineral acid?

1. Hydrochloric acid
2. Citic acid
3. Sulphuric acid
4. Nitric acid

Answer: 2. Citic acid

Question 23. Which among the following is not a base?

1. NaOH
2. KOH
3. NH₄OH
4. C₂H₅OH

Answer: 4.  C₂H₅OH

Question 24. Which ofthe following statements is not correct?

1. All metal carbonates react with acid to give a salt, water and carbon
   dioxide
2. All metal oxides react with water to give salt and acid
3. Some metals react with acids to give salt and hydrogen
4. Some non-metal oxides react with water to form an acid

Answer: 2.  All metal oxides react with water to give salt and acid

Question 25. Match the chemical substances given in Column (A) with their appropriate application given in Column (B)

1. 1-B,2-A,3-D,4-C
2. 1-C,2-B,3-D,4-A
3. 1-C,2-D,3-1,4-2
4. 1-B,2-D,3-A,4-C

Answer: 3.  1-C,2-D,3-1,4-2

Question 26. Equal volumes of hydrochloric acid and sodium hydroxide solutions of the same concentration are mixed and the pH of the resulting solution is checked with pH paper. What would be the colour obtained? (You may use the colour guide given below.)

1. Red
2. Yellowish-orange
3. Yellowish green
4. Blue

Answer: 3. Yellowish green

Question 27. Which ofthe following is(are) true when HCl(g) is passed through water?

1. It does not ionise in the solution as it is a covalent compound.

2. It ionises in the solution

3. It gives both hydrogen and hydroxyl ions in the solution

4. It forms hydronium ions in the solution due to the combination of hydrogen ions with a water molecule

1. 1 only
2. 3 only
3. 2 and 4
4. 3 and 4

Answer: 3. 2 and 4

Question 28. Which of the following statements is true for acids’?

1. Bitter and change red litmus to blue
2. Sour and change red litmus to blue
3. Sour and change blue litmus to red
4. Bitter and change blue litmus to red

Answer: 3. Sour and change blue litmus to red

Question 29. Which ofthe following are present in a dilute aqueous solution of hydrochloric acid?

1. H₃O⁺+ Cl^–
2. H₃O⁺+ OH^–
3. Cl^– + OH^–
4. Unionised HCl

Answer: 1. H₃O⁺+ Cl^–

Question 30. Identify the correct representation ofreaction occurring during the chlor-alkali process

1. 2NaCl(l) + 2H₂O(l) → 2NaOH(Z) + Cl₂(g) + H₂(g)
2. 2NaCl(aq) + 2H₂O(aq)→  2NaOH(aq) + Cl₂(g) + H₂(g)
3. 2NaCl(aq) + 2H₂O(l) → 2NaOH(ag) + Cl₂(aq) + H₂(aq)
4. 2NaCl(aq) + 2H(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

Answer: 4.  2NaCl(aq) + 2H₂O(l) → 2NaOH(ag) + Cl₂(aq) + H₂(aq)

Question 31. Match the given in Column (A) with the correct source given in Column (B)

Answer: 1-D ,2-C ,3- B ,4-A

Question 32. Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)

Answer: 1- B, 2-C, 3- D,4- A

Question 33. A solution turns red litmus blue. ItspH is likely to be

1. 1
2. 4
3. 5
4. 10

Answer: 4. 10

Question 34. A solution reacts with crushed eggshells to give a gas that turns lime-water milky. The solution contains

1. NaCl
2. HCl
3. LiCl
4. KCl

Answer: 4. KCl

Question 35. 10 mL ofa solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be

1. 4 mL
2. 8 mL
3. 12 mL
4. 16 mL

Answer: 4. 16 mL

Question 36. Which one ofthe following types of medicines is used for treating indigestion?

1. Antibiotic
2. Analgesic
3. Antacid
4. Antiseptic

Answer: 3. Antacid

CBSE Class 10 Science Class 10 Science Chapter 1 Chemical Reactions And Equations

Representation of Chemical Reaction

CBSE Class 10 Science Class 10 Science Chapter 1 Chemical Reactions And Equations Definitions

1. Chemical reaction: Whenever a chemical change occurs, we can say that a chemical reaction occurs.

2. The following observations help us determine whether a chemical reaction occurred.

1. Change in state
2. Change in colour
3. Evolution of a gas
4. Change in temperature

3. Chemical equation: A chemical change can be represented symbolically in terms of a chemical equation.

Read and Learn More CBSE Class 10 Science Short Answer Questions

4. A chemical equation represents a chemical reaction occurring in a chemical change.

5. To make a chemical reaction more informative, the physical states of the reactants and products are mentioned along with their chemical formulae. The gaseous, liquid, aqueous and solid states of reactants and products are represented by notations (g), (l), (aq) and (s) respectively.

6. Mass can neither be created nor destroyed in a chemical reaction, that is, the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.

7. Balancing equation: A chemical reaction is balanced so that the number of atoms to each element involved in a chemical reaction is the same on the reactant and product sides.

8. Combination reaction: The reaction in which two or more substances combine to form a new single substance.

For example:

⇒ \(\underset{\text { Calcium oxide(Quicklime) }}{\mathrm{CaO}(s)}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}(l)} \longrightarrow \underset{\text { Calcium hydroxide(Slaked lime) }}{\mathrm{Ca}(\mathrm{OH})_2(a q)}\)

9. Decomposition reaction:

The reaction in which a single substance decomposes to give two or more substances. It can be thermal (by heat) electrolytic (by electric current) decomposition or photochemical (by sunlight). For example,

2 Pb (NO)₂(s) (Lead nitrate) →  (heat) → 2 PbO(s)(Lead oxide)  + 4 NO₂ (g) +O₂(g)

10. Displacement reaction:

The chemical reaction in which an element displaces another element from its compound.

For example:

⇒ \(\underset{\text { Iron }}{\mathrm{Fe}(s)}+\underset{\text { Copper sulphate }}{\mathrm{CuSO}_4(a q)} \longrightarrow \underset{\text { Iron sulphate }}{\mathrm{FeSO}_4(a q)}+\underset{\text { Copper }}{\mathrm{Cu}(s)}\)

11. Double displacement reaction:

The reaction is in which two different atoms or groups of atoms (ions) are mutually exchanged.

For example:

⇒ \(\underset{\text { Sodium sulphate }}{\mathrm{Na}_2 \mathrm{SO}_4(a q)}+\underset{\text { Barium chloride }}{\mathrm{BaCl}_2(a q)} \rightarrow \underset{\text { Barium sulphate }}{\mathrm{BaSO}_4(s)}+\underset{\text { Sodium chloride }}{2 \mathrm{NaCl}(a q)}\)

12. Precipitation reaction: The reaction that produces precipitation (insoluble salt) is called precipitation reaction.

For example:

⇒ \(\underset{\text { Silver nitrate }}{\mathrm{AgNO}_3(a q)}+\underset{\text { Sodium chloride }}{\mathrm{NaCl}(a q)} \longrightarrow \underset{\begin{array}{c}
\text { Silver chloride } \\
\text { (white pott }
\end{array}}{\mathrm{AgCl}(s)}+\underset{\text { Sodium nitrate }}{\mathrm{NaNO}_3(a q)}\)

13. Neutralisation reaction: When acids react with bases or alkalis their acidity is destroyed and a salt is produced; such reactions are known as neutralisation reactions.

For example:

⇒  \(\underset{\begin{array}{c}
\text { Hydrochloric } \\
\text { acid }
\end{array}}{\mathrm{HCl}}+\underset{\text { Sodium hydroxide }}{\mathrm{NaOH}} \longrightarrow \underset{\text { Sodium chloride }}{\mathrm{NaCl}}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}}\)

14. Isomerisation reaction:

Those reactions in which the atoms present in the molecules of the reactant are rearranged are known as isomerisation reactions.

For example:

NH₄CNO(Ammoniumcyanate) →(heat) → H₄N-CO-NH₄(urea)

15. Photochemical reaction: The reaction which takes place in the presence of light is called photochemical reaction.

For example:

2AgBr(s) (silver bromide) → (sunlight) → 2 Ag(Silver) +Br₂ (Bromine)

16. Exothermic reaction: The reaction in which heat is given out along with the products.

⇒ \(\underset{\text { Carbon }}{\mathrm{C}(\mathrm{s})}+\underset{\text { Oxygen }}{\mathrm{O}_2(\mathrm{~g})} \longrightarrow \underset{\text { Carbon dioxide }}{\mathrm{CO}_2(\mathrm{~g})}+\text { Heat }\)

17. Endothermic reaction: The reaction in which energy is absorbed by the reactants.

N₂(g)(Nitrogen) +O₂(g)(oxygen) → (heat) →  2NO(g) (Nitric oxide)

18. Oxidation: It is the gain of oxygen or the loss of hydrogen.

For example:

2 Cu (Copper) +O₂(Oxygen) → (heat)→ 2CuO(Copper oxide)

19. Reduction: It is the loss of oxygen or gain of hydrogen. For example

CuO(Copper oxide) +H₂ → (heat)→ Cu (Copper)  +HO(water)

20. Redox reaction: The reaction in which one reactant gets oxidised while the other gets reduced.

21. Oxidising agent: The substance which helps in oxidation is called oxidising agent.

22. Reducing agent: The substance which helps in reduction is called reducing agent.

23. Corrosion: When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.

For example:

1. The reddish-brown coating on iron
2. The black coating on the silver
3. The green coating on the copper

24. Rancidity: When fats and oils are oxidised, they become rancid and their smell and taste change.

25. Antioxidants: The substances which prevent oxidation are added to foods containing fats and oils

CBSE Class 10 Science Class 10 Science Chapter 1 Chemical Reactions And Equations Short Question And Answers

Question 1. Why should a magnesium ribbon be cleaned before burning in the air?
Answer:

On exposure to air magnesium ribbon gets covered with a layer of magnesium carbonate. So magnesium ribbon should be cleaned with as and paper so that only clean magnesium ribbon is available for burning in air.

Question 2. Write the balanced equation for the following chemical reactions.

1. Hydrogen + Chlorine → Hydrogen chloride
2. Barium chloride + Aluminium sulphate chloride → Barium sulphate + Aluminium
3. Sodium + Water  →  Sodium Hydroxide +Hydrogen

Answer:

1. H₂ + Cl₂ → 2 HCl

2. 3BaCl₂ + Al₂ (SO₄)₃ → 3BaSO₄ + 2AlCl

3. 2Na + 2H₂O→  2NaOH₄+ H₂

Question 3. Write a balanced chemical equation with state symbols for the following reactions.

1. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
2. Sodium hydroxide solution (in water) reacts with a hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Answer:

1. BaCl₂(aq) (Barium chloride) + Na₂SO₄(aq) (Sodiumsulphate)→ BaSO₄(s)(Barium sulphate)+2 NaCl (aq)(Sodium chloride

2. NaOH(aq) (Sodium hydroxide)+ HCl(sq) (Hydrochloric acid) → NaCl(aq) (Sodium chloride)  + H₂O(Water)

Question 4. A solution ofa substance ‘X? is used for whitewashing.

1. Name the substance ‘X and write its formula.
2. Write the reaction ofthe substance ‘X’ named in (i) above with water.

Answer:

1. X is quick lime and its formula is CaO.

2. CaO(s) (Quick lime) +H₂O(Water) → Ca(OH)₂(aq)(Slakedlime or calcium hydroxide)

Question 5.  Why is the amount of gas collected in one of the test tubes double the amount collected in the other? Name this gas.
Answer:

Water containing a few drops of dilute sulphuric acid is electrolysed using graphite anode and cathode. H₂ gas is collected at the cathode and oxygen at the anode.

The electrochemical reaction is:

2HO(l) → 2H₂(g)+O₂(g)

Thus the amount of hydrogen gas collected is double that of oxygen. If the two gases are collected in two different test tubes, the gas collected in one test tube (i.e., H₂) is double that collected in the other test tube (i.e., oxygen).

Question 6. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer:

This is a displacement reaction.

Fe(s)(Iron nail)+ CuSO₄(aq)  → FeSO₄(aq) + Cu(s) (Copper)

Since copper sulphate is blue in colour and iron sulphate is greenish, the colour of copper sulphate changes when an iron nail is dipped in it.

Question 7. Give an example of a double displacement reaction other than the one given in
Answer:

AgNO₃(ag)(Silver nitrate ) + NaCl(aq)(Sodium chloride ) →  AgCl(s)(Silver chloride) + NaNO₃(aq)(Sodium nitrate)

Thus silver exchanges chloride from sodium chloride, and sodium chloride exchanges nitrate ions from silver nitrate. This is a double displacement reaction.

Question 8. Identify the substances that are oxidised and the substances that are reduced in the following reactions.

1. 4Na(s) + O₂(g) →  2Na₂O(s)
2. CuO(s) + H₂(g) →  Cu(s) + H₂O(Z)

Answer:

1. Na(s) is oxidised to Na₂O
2. (s) and oxygen is reduced to O^2- (NaO₂(s)).
3. CuO(s) is reduced to Cu(s) and H₂(g) is oxidised to H₂O(Z).

Question 9. What is a balanced chemical equation? Why should chemical equations be balanced1
Answer:

In a balanced equation the number ofatoms ofeach element on both sides ofthe equation are equal. The chemical equation must be balanced with the aspect of mass because matter can neither be created nor destroyed.

The equation must be balanced concerning charge because the electrons lost by atoms to form cations are equal to electrons gained by other atoms to form anions. Free electrons do not exist in solution.

Question 10. Write the balanced chemical equations for the following reactions:

1. Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
2. Zinc + Silver nitrate → Zinc nitrate + Silver
3. Aluminium + Copper chloride → Aluminium chloride + Copper
4. Barium chloride + Potassium sulphate → Barium, sulphate + Potassium chloride

Answer:

Ca(OH)₂+ CO₂ → CaCO₃ + H₂O

Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

2Al + 3CuCl → 2AlCl₃ + 3Cu

BaCl₂+ K₂SO₄  → 4 BaSO₄ + 2KCl

Question 11. Why is respiration considered an exothermic reaction? Explain.
Answer:

During digestion, food is broken down into simpler substances. Food like rice, potatoes and bread are made up of carbohydrates. These carbohydrates are further broken down into glucose. Glucose during respiration (inhalation of oxygen) is oxidised with the

Liberation of energy as shown below:

C₆H₁₂ O₆ (Glucose)+ 6O₂(aq)(Oxygen) + 6CO₂(aq)  → 6CO₂  (Carbon dioxide)(aq) + 6H₂O(l) (Water)+ energy

Thus, respiration is an exothermic process.

Question 12. In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.
Answer:

The involved reaction is:

⇒ \(\mathrm{Cu}(s)+2 \mathrm{AgNO}_3(a q) \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2(a q)+2 \mathrm{Ag}(s)\)

Question 13. What do you mean by a precipitation reaction? Explain by giving an example.
Answer:

When two reactants in a solution react and one or more of the products are insoluble or form a precipitate, the reaction is called a precipitation reaction.

For example, when a solution of iron chloride and ammonium hydroxide is mixed, a brown precipitate of iron hydroxide is formed.

FeCl₃(aq)(Ferric chloride) + 3NH₄OH(aq)(Ammoniumhydroxide) → Fe(OH)₃(s) (Ferriuc hydroxide)  +3NH₄Cl(aq) (Ammonium chloride)

Question 14. Why do we apply paint on iron articles?
Answer:

It is observed that iron articles are shiny when new but get coated with a reddish-brown surface when left for some time as the iron articles get rusted. This process is called corrosion. To prevent rusting of iron, paint is applied on iron articles.

Question 15. What happens chemically when quicklime is added to water filled in a bucket?
Answer:

Quicklime reacts with water to form slaked lime and produces a lot of heat and hissing sound

⇒ \(\underset{\begin{array}{c}
\text { Quicklime } \\
\text { (Calcium oxide) }
\end{array}}{\mathrm{CaO}(s)}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}(l)} \longrightarrow \underset{\begin{array}{c}
\text { Slaked lime } \\
\text { (Calcium hydroxide) }
\end{array}}{\mathrm{Ca}(\mathrm{OH})_2(s)}+\text { Heat + Hissing sound }\)

Question 16. Study the reactions given below. State which of the following chemical reactions will take place or not, giving suitable reason for each:

1. Zn(s) + CuSO₄  (aq) → ZnSO₄(aq) + Cu(s)
2. Fe(s) + ZnSO₄(aq)→ FeSO₄(aq) + Zn(s)
3. Zn(s) + FeSO₄(aq) →  ZnSO₄(aq) + Fe(s)

Answer:

1. Zinc is more reactive than copper; so it will displace copper from CuS04. This reaction will take place.
2. Iron is less reactive than zinc, so it cannot displace zinc from zinc sulphate. The reaction will not take place.
3. Zinc is more reactive than iron, it will displace iron from FeS04. The reaction will take place.

Question 17. What is meant by the skeletal-type chemical equation? What does it represent? Using the equation for electrolytic decomposition ofwater, differentiate between a skeletal chemical equation and a balanced chemical equation.
Answer:

The equations in which gaseous are written in atomic form instead of molecular form and the equation is not balanced are called skeletal type chemical equations.

They represent gaseous elements formed in the atomic state and the equation is not balanced

⇒ \(\mathrm{H}_2 \mathrm{O}→ {\text { Electrolysis }} →\mathrm{H}+\mathrm{O} \text { (Sketal equation) }\)

Hydrogen and oxygen are written in atomic forms and the equation is not balanced.

H₂ O → 2H₂ + O₂ (Balanced chemical equation)

H₂ O → H₂ + O₂ is the Skeletal equation.

Question 18. What is redox reaction? When a magnesium ribbon burns in the air with a dazzling flame and forms white ash, is magnesium oxidised or reduced? Why?
Answer:

The reaction in which oxidation (loss ofelectrons) and reduction (gain of electrons) take place simultaneously is called a redox reaction.

⇒ \(\underset{\text { Magnesium }}{2 \mathrm{Mg}(s)}+\underset{\text { Oxygen }}{\mathrm{O}_2(g)} \longrightarrow \underset{\text { Magnesium oxide }}{2 \mathrm{MgO}(s)}\)

Magnesium is getting oxidised because it is losing electrons from Mg²⁺ and oxygen is gaining electrons to form O^2- therefore it is getting reduced.

Question 19. Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions:

1.  HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
2. Fe(s) + CuSO₄(aq) → FeSO₄(aq) +Cu(s)

Answer:

A displacement reaction is a reaction in which more reactive metal can displace less reactive metal from its salt solution.

Double displacement reaction: The reaction is in which a compound exchanges its ions to form two new compounds called double displacement reaction.

1. Double displacement reaction
2. Displacement reaction

Question 20.

1. When a metal ‘X’ is added to the salt solution ofa metal Y following chemical reaction takes place: Metal X + Salt solution of ‘Y’→ Salt solution of ‘X’ + Metal ‘Y’

2. Mention the inference you draw regarding the reactivity of metals ‘X and Y’ and also about the type of reaction. State the reason for your conclusions.
Answer:

It is a displacement reaction.

1. Metal X is more reactive than metal Y.
2. Metal X is displacing metal Y from its salt solution.

A more reactive metal displaces a less reactive one from its salt solution. X is more reactive than Y.

Question 21. Write the essential condition for the following reactions to take place: 2Ag + Cl₂ and write one use of this reaction.
Answer:

1. To carry out the reaction 2AgCl → 2Ag + Cl₂ presence ofsunlight is essential.

This reaction is used in black-and-white photography

Question 22. Name the reducing agent in the following reaction

3MnO₂ + 4Al → 3Mn + 2Al₂O₃

State which is more reactive, Mn or Al and why?

Answer:

‘Al’ is a reducing agent.

‘Al’ is more reactive than Mn.

∴ ‘Al’ displaces Mn from its oxide.

Question 23. Identify the type ofreaction from the following equations.

1. CH₄ + 2O₂ → CO₂ + 2H₂O
2. Pb(NO₃)₂+ 2KI→ Pbl₂+ 2KNO₃
3. CaO + H₂O→ Ca(OH)₂
4. CuSO₄ + Zn→ZnSO₄ + Cu

Answer:

1. Combustion reaction
2. Double displacement reaction
3. Combination reaction
4. Displacement reaction

Question 24. Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
Answer:

Any two of these observations will suggest a chemical reaction has taken place

1. Change in state
2. Change in colour
3. Evolution of gas
4. Change in temperature

For example, lead nitrate is a white crystalline solid, on heating it gives a yellowish-brown solid (lead monoxide), brown gas is evolved and a colourless gas is evolved.

It shows chemical reaction has taken place.

Question 25. State what changes in the colour of the iron nail and copper sulphate solution are observed when an iron nail is dipped into copper sulphate solution for about 20 minutes. Write the equation for the reaction that takes place. Also, name the type ofreaction involved in the above process.
Answer:

1. The iron nail becomes brownish and the blue colour of the copper sulphate solution fades.
2. Fe(s) + CuSO₄(aq)→  FeSO₄(aq) + Cu(s)
3. Displacement reaction

Question 26. What is observed when a solution of potassium iodide is added to a solution of lead nitrate? Name the type ofreaction. Write a balanced chemical equation to represent the above chemical reaction.
Answer:

A yellow precipitate of lead iodide is formed. It is a precipitation reaction.

Pb(NO₃)₂ (aq) + 2KI (aq)→Pbl₂ (s) + 2KNO₃ (aq)

It is also called a double displacement reaction.

Question 27. Explain giving chemical equation of any two uses of chemical decomposition reaction in industry.
Answer:

1. In manufacturing cement, quicklime is used and it is obtained by thermal decomposition of limestone.

CaCO₃(s) → (Heat) →CaO(s) + CO₂(g)

2. In manufacturing photochromic glass, silver chloride/bromide is used which turns grey in sunlight.

Question 28. 2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer the following:

1. State the colour ofthe fumes evolved and the residue left.
2. Name the type of chemical reaction that has taken place stating its balanced chemical equation.

Answer:

1. Brown-coloured fumes of NO₂ gas are evolved and a yellowish-brown residue is formed.

2. Decomposition reaction has taken as,

2Pb(NO₃)₂(s) → (Heat) → 2PbO(s)+4NO₂(g)+ O₂(g)

Question 29. What is meant by a balanced chemical equation? Why chemical equations are balanced? Balance the chemical equation given below:

Al₂O₃ + NaOH→ NaAlO₂ + H₂O

Answer:

A chemical equation in which the number of atoms of each type involved is the same on the reactants and products is called a balanced chemical equation.

To justify the law of conservation of mass in a reaction, a chemical equation is to be balanced.

Al₂O₃ + 2NaOH→ 2NaAlO₂ + H₂O

Question 30. What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the action and name the type ofreaction.
Answer:

A white precipitate of barium sulphate is formed.

If both reactants are in solid state, the reaction will not take place between them.

BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

It is a double displacement as well as a precipitation reaction.

Question 31. Write balanced chemical equations for the following reactions.

1. Silver bromide on exposure to sunlight decomposes into silver and bromine.
2. Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.

Answer:

1. 2AgBr(s) →  (Sunlight) → 2Ag(s)+Br(g)

2. 2Na(s) + 2H₂O(l)→ 2NaOH(aq) + H₂(g)

Question 32. Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.
Answer:

Thermal decomposition reaction

(Copper carbonate -Green)CuCO(s)→ (Heat) → CuO(s)(Copper oxide -Black)+CO₂(g)

Photochemical decomposition reaction

2 AgCl(s) → (Sunlight) → 2 Ag(s)+Cl₂(g)

Question 33.

1. Why is a combustion reaction an oxidation reaction?
2. How will you test whether the gas evolved in a reaction is hydrogen? 

Answer:

1. A combustion reaction is an oxidation reaction because it is always carried in the presence of air or oxygen.

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

2. Bring a burning matchstick close to the mouth ofthe tube from which hydrogen gas escapes. The gas will immediately catch fire and this will be accompanied by a pop sound.

Question 34. An aluminium can was used to store the ferrous sulphate solution. It is observed that in a few days, holes appeared in the can. Explain the observation and write a chemical equation to support your answer.
Answer:

Aluminium being more reactive displaces ferrous ions from ferrous sulphate solution and this results in the appearance of holes in the aluminium can.

⇒ \(2 \mathrm{Al}(s)+\underset{\text { (Ferrous sulphate) }}{3 \mathrm{FeSO}_4(a q)} \longrightarrow \underset{\text { (Aluminium sulphate) }}{\mathrm{Al}_2\left(\mathrm{SO}_4\right)_3(a q)}+3 \mathrm{Fe}(s)\)

Question 35. Identify the type ofreaction from the following equations:

1. CH₄ + 2O₂-4 →  CO₂ + 2H₂O
2. Pb(NO₃)₂ + 2KI→  Pbl₂ + 2KNO₃
3. CaO + H₂O→ Ca(OH)₂
4. CuSO₄ + Zn→ ZnSO₄ + Cu

Answer:

1. Combustion reaction and oxidation reaction

2. Double displacement and precipitation reaction

3. Combination reaction

4. Displacement reaction

Question 36.

1. A solution of substance ‘X’ is used for whitewashing. What is substance ‘X? State the chemical reaction of X’ with water.

Why does the colour of copper sulphate solution change when an iron nail is dipped in it? 
Answer:

‘X’ is calcium oxide (CaO)

CaO(s) + H₂O(l)→  Ca(OH)₂(aq) + Heat

It is because iron displaces copper from CuS04 to form FeSO₄ which is pale green

Question 37. Using a balanced chemical equation explain the difference between a displacement reaction and a double displacement reaction.
Answer:

In a displacement reaction, more reactive metal can displace less reactive metal from its salt solution

Example:  Cu(s) + 2AgNO(aq)→ Cu(NO₃)₂(aq) + 2Ag(s)

In a double displacement reaction, two compounds exchange their ions to form two new compounds,

Example: NaOH + MCI→ NaCl + H₂O

Question 38. When you have mixed the solutions of lead (II) nitrate and potassium iodide

1. What was the colour ofthe precipitate formed and can you name the precipitate?
2. Write the balanced chemical equation for this reaction.
3. Is this also a double displacement reaction?

Answer:

The colour of the precipitate is yellow. The name of the compound formed as a precipitate is lead iodide (Pbl₂).

Pb(NO₃)₂ (aq) + 2KI(aq)→ Pbl₂(s) + 2KNO₃(aq)

Yes, it is also a double displacement reaction.

Question 39. Balance the following chemical equations:

1. BaCl₂ + H₂SO₄ → BaSO₄ + HCl
2. Ca(OH)₂ + HNO₃→ Ca(NO₃)₂ + H₂O
3. Pb(NO₃)₂→ PbO + NO₂ +O₂
4. MnO₂ + HCl→MnCl₂ + H₂O + Cl₂

Answer:

1. BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl
2. Ca(OH)₂ + 2HNO₃→ Ca(NO₃)₂ + 2H₂O
3. 2Pb(NO₃)₂→ 2PbO + 4NO₂ +O₂
4. MnO₂ + 4HCl→MnCl₂ + 4H₂O + Cl₂

Question 40. Define combination reaction. Give one example ofa combination reaction which is also exothermic.
Answer:

A reaction in which two elements or compounds combine to form a single compound is called a combination reaction.

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

It is also an exothermic reaction because heat is evolved.

Question 41. Write the balanced chemical equations for the following reactions.

1. Sodium carbonate in reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen carbonate.
2. Sodium hydrogen carbonate in reaction with hydrochloric acid gives sodium chloride, and water and liberates carbon dioxide.
3. Copper sulphate on treatment with potassium iodide precipitates cuprous iodide(Cu₂I₂), liberates iodine gas and also forms potassium sulphate.

Answer:

1. Na₂CO₃ + HCl → NaCl + NaHCOg
2. NaHCO₃ + HCl → NaCl + H₂O+ CO₂
3. 2CuSO₄ + 4Kl→Cu₂I₂ + 2K₂SO₄ + I₂

Question 42. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type ofthe chemical reaction.
Answer:

KCl(aq) + AgNO₃ →AgCl(s) ↓ + KNO₃(aq)

Double displacement and precipitation reaction

Question 43. Ferrous sulphate decomposes with the evolution of gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.
Answer:

2FeSO(s) → (Heat) → 2Fe₂SO₃(s) + SO₂(g) + SO₃(g)

It is an example of a thermal decomposition reaction.

Question 44. Why do fireflies glow at night?
Answer:

Fireflies have a protein which in the presence ofan enzyme undergoes aerial oxidation.

This is a chemical reaction which involves the emission of visible light.
Therefore, fireflies glow at night.

Question 45. Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Answer:

Grapes when attached to the plants are living and therefore their immune system prevents fermentation. The microbes can grow in the plucked grapes and under anaerobic conditions, these can be fermented. This is a chemical change.

Question 46. Which among the following are physical or chemical changes?

1. Evaporation of petrol
2. Burning liquefied Petroleum Gas (LPG)
3. Heating of iron rod to red hot
4. Curdling of milk
5. Sublimation of solid ammonium chloride

Answer:

1. 1, 3 and 5 are physical changes.
2. 2 and 4 an’ chemical changes

Question 47. A substance X, which is an oxide of group 2 element is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution which turns red litmus blue. Identify and also write the chemical reaction involved.
Answer:

The name of the substance is Calcium oxide.

CaO + H₂ (l) → Ca(OH)(aq)

Question 48. Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why1.
Answer:

Zinc is more reactive than copper.

Zn + 2HCl → ZnCl₂ + H₂

Al + HCl →   No reactions.

Question 49. A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.

1. Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
2. Name the black substance formed and give its chemical formula.

Answer:

1. Metals such as silver when attacked by substances around it such as moisture, acids, gases, etc, are said to corrode and this phenomenon is called corrosion.
2. The black substance is formed because silver (Ag) reacts with H₂S present in the air. It forms a thin black coating of silver sulphide (Ag₂S).

Question 50. Give reasons why:

1. Sodium acts as a reducing agent while chlorine acts as an oxidising agent in the following reaction: 2Na+Cl → 2 NaCl(s)
2. White-coloured silver chloride turns grey when kept in sunlight.

Answer:

1. Sodium reduces chlorine atoms to chloride ions, therefore it acts as a reducing agent while chlorine oxidises sodium atoms to sodium ions, therefore it acts as an oxidising agent.
2. This is due to the decomposition of silver chloride into silver and chlorine by light.

Question 51. Give one example of a combination reaction in which an element combines with a new compound to give a new compound
Answer:

8NH₃ + 3Cl₂ → 6NH₄Cl + N₂

O₂ + 2SO₂ →  2SO₃

CBSE Class 10 Science Class 10 Science Chapter 1Chemical Reactions And Equations Multiple Choice Questions

Question 1. Which of the following is not a physical change?

1. Boiling of water to give water vapour
2. Melting of ice to give water
3. Dissolution of salt in water
4. Combustion liquefied Petroleum Gas (LPG)

Answer: 4. Combustion liquefied Petroleum Gas (LPG)

Question 2. The following reaction is an example ofa

4NH₃(g) + 5O₂(g)→4NO(g) + 6H₂O(g)

1. Displacement reaction

2. Combination reaction

3. Redox reaction

4. Neutralisation reaction

1. 1 and 4
2. 2 and 3
3. 1 and 3
4. 3 and 4

Answer: 4.  3 and 4

Question 3. Which of the following statements about the given reaction are correct?

3Fe(s) + 4H₂O(g) > Fe₃O₄) + 4H₂(g)

1. Iron metal is getting oxidised

2. Water is getting reduced

3. Water acts as a reducing agent

4. Water acts as an oxidising agent

1. 1, 2 and 3
2. 3 and 4
3. 1, 2 and 4
4. 2 and 4

Answer: 3. 1, 2 and 4

Question 4. Which of the following are exothermic processes?

1. Reaction of water with quick lime

2. Dilution of an acid

3. Evaporation of water

4. Sublimation of camphor (crystals)

1. 1 and 2
2. 2 and 3
3. 1 and 4
4. 3 and 4

Answer: 1. 1 and 2

Question 5. Three beakers labelled as A, B, and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuS04 and NaCl were added to the beakers A, B, and C respectively.  It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in the case of beaker C, the temperature of the solution fell. Which one of the following statement(s) is (are) correct?

1. In beakers A and B, an exothermic process has occurred.

2. In beakers A and B, an endothermic process has occurred.

3. In beaker C exothermic process has occurred.

4. In beaker C endothermic process has occurred.

1. 1 Only
2. 2 Only
3. 1 and 4
4. 2 and 3

Answer: 3.  1 and 4

Question 6. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate. The light purple colour of the solution fades and finally disappears. Which ofthe following is the correct explanation for the observation?

1. KMnO₄ is an oxidising agent, it oxidises FeSO₄
2. FeSO₄ acts as an oxidising agent and oxidises KMnO₄
3. The colour disappears due to dilution: no reaction is involved
4. KMnO₄ is an unstable compound and decomposes in the presence of FeSO₄ to a colourless compound.

Answer: 1. KMnO₄ is an oxidising agent, it oxidises FeSO₄

Question 7. Which among the following is (are) double displacement reaction(s)?

1. Pb + CuCl₂→ PbCl₂ + Cu

2. Na₂SO₄ + BaCl₂→  BaSO₄+ 2NaCl

3. C +O₂ → CO₂

4. CH₄ + 2O₂→ CO₂ + 2H₂O

1. 1 and 4
2. 2 Only
3. 1 and 2
4. 3 and 4

Answer: 2.  2 Only

Question 8. Which among the following statements) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to

1. The formation of silver by decomposition of silver chloride

2. Sublimation of silver chloride

3. Decomposition of chlorine gas from silver chloride

4. Oxidation of silver chloride.

1. 1 only
2. 1 and 3
3. 2 and 3
4. 4 only

Answer: 1.  1 only

Question 9. Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking oflime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about the slaking of lime and the solution formed?

1. It is an endothermic reaction

2. It is an exothermic reaction

3. The pH ofthe resulting solution will be more than seven

4. The pH ofthe resulting solution will be less than seven

1. 1 and 2
2. 1 and 3
3. 1 and 4
4. 4 only

Answer: 2.  1 and 3

Question 10. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which ofthe following correctly represents the type ofthe reaction involved?

1. Displacement reaction

2. Combination reaction

3. Precipitation reaction

4. Double displacement reaction

1. 1 only
2. 2 only
3. 4 only
4. 2 and 4

Answer: 4.  2 and 4

Question 11. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during the electrolysis of water is

1. 1:1
2. 2: 1
3. 4:1
4. 1:2

Answer: 2.  2: 1

Question 12. Which ofthe following is(are) an endothermic process(es)?

1. Dilution of sulphuric acid

2. Sublimation of dry ice

3. Condensation of water vapours

4. Evaporation of water

1. 1 and 3
2. 2 only
3. 3 only
4. 2 and 4

Answer: 4.  2 and 4

Question 13. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which ofthe following can be used in place of lead nitrate?

1. Lead sulphate (insoluble)
2. Lead acetate
3. Ammonium nitrate
4. Potassium sulphate

Answer: 2.  Lead acetate

Question 14. Which of the following gases can be used for storage of fresh samples of oil for a long time?

1. Carbon dioxide or oxygen
2. Nitrogen or oxygen
3. Carbon dioxide or helium
4. Helium or nitrogen

Answer: 4.  Helium or nitrogen

Question 15. The following reaction is used for the preparation of oxygen gas in the laboratory

3Fe(s) + 4H₂ O(g)→ Fe₃ O₄ (s) + 4H₂ (g)

Which of the following statement (s) is(arc) correct about the reaction?

1. It is a decomposition traction and endothermic
2. It is u i’ombinntion traction
3. It is (i decomposition reaction accompanied by the release of heat
4. It is a photochemical decomposition reaction and exothermic

Answer: 1.  It is a decomposition traction and endothermic

Question 16. Which one ofthe following processes involves chemical reactions?

1. Storing ofoxygen gas under pressure in a gas cylinder
2. Liquefaction ofair
3. Keeping petrol in a china dish in the open
4. Heating copper wire in presence ofair at high temperature

Answer: 4.  Heating copper wire in the presence ofair at high temperature

Question 17. In which of the following chemical equations, do the abbreviations represent the correct states ofthe reactants and products involved at reaction temperature?

1. 2H₂(l) + O₂(Z)→2H₂O(g)
2. 2H₂(g) +O₂(l) → 2H₂O(l)
3. 2H₂(g) + O₂(g)→ 2H₂O(l)
4. 2H₂(g) + O₂(g)→ 2H₂O(g)

Answer: 3.  2H₂(g) + O₂(g)→ 2H₂O(l)

Question 18. Which of the following are combination reactions?

1. \(2 \mathrm{KCIO}_3 →{\text { Heat }}→ 2 \mathrm{KCI}+30_2\)

2. \(\mathrm{MgO}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Mg}(\mathrm{OH})_2\)

3. \(4 \mathrm{Al}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{Al}_2 \mathrm{O}_3\)

4. \(\mathrm{Zn}+\mathrm{FeSO}_4 \longrightarrow \mathrm{ZnSO}_4+\mathrm{Fe}\)

1. 1 and 3
2. 3 and 4
3. 2 and 4
4. 2 and 3

Answer: 4.  2 and 3

Question 19. Which ofthe statements about the reaction below are incorrect?

2PbO(s) + C(s)→ 2Pb(s) + CO₂(g)

1. Lead is getting reduced.

2. Carbon dioxide is getting oxidised.

3. Carbon is getting oxidised.

4. Lead oxide is getting reduced.

1. 1 and 2
2. 1 and 3
3. 1, 2 and 3
4. All

Answer: 1 and 2 are incorrect.

Question 20. Fe₂O₃ + 2Al  → Al₂O₃ + 2Fe

The above reaction is an example of a:

1. Combination reaction
2. Double displacement reaction
3. Decomposition reaction
4. Displacement reaction

Answer: 4. Displacement reaction

Question 21. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

1. Hydrogen gas and iron chloride are produced.
2. Chlorine gas and iron hydroxide are produced.
3. No reaction takes place.
4. Iron salt and water are produced.

Answer: 1. Hydrogen gas and iron chloride are produced.

CBSE Class 10 Science Chapter 4 Carbon And Its Compounds Very Short Question And Answers

Question 1. Name the element, other than carbon, which exhibits the property of catenation up to seven or eight atoms. Are these compounds stable?
Answer: Silicon. No, they are very reactive.

Question 2. What are oxidizing agents?
Answer: An oxidizing agent oxidizes other substances by providing oxygen or removing hydrogen

Question 3. What change will you observe if you test soap with litmus paper (red and blue)?
Answer: When we test soap with red and blue litmus paper: red will turn blue but blue will remain as blue.

Question 4. Would you be able to check if water is hard by using a detergent?
Answer: No, detergent cannot be used to check if water is hard.

Question 5. The formula of a hydrocarbon is CnH2n. Name the family to which it belongs and also predict its nature.
Answer: The hydrocarbon belongs to the alkene family. It is unsaturated.

Question 6. An unknown compound has the smell of vinegar. Identify it.
Answer: The compound is ethanoic acid also called acetic acid.

Read and Learn More CBSE Class 10 Science Very Short Answer Questions

Question 7. What do we get when ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid?
Answer:  Ethyl ethanoate (CH₃ COOC₂H₅) is formed by esterification reaction. It has a fruity smell.

Question 8. How is scum formed? 
Answer:  When soap reacts with hard water, the minerals present in water react with soap and form a white curdy substance known as scum. It reduces the cleaning ability of soap.

Question 9. Draw the electron dot structure of ethane
Answer:

Electron dot structure of ethane:

Question 10. Why do carbon compounds not conduct electricity?
Answer: Since carbon, compounds do not give rise to any ions or charged particles in a molten state or aqueous solutions.

Question 11. Which two of the following compounds belong to the same homologous series
Answer: C₂H₆O, CH₄O.

Question 12. Why are organic compounds present in such a large number?
Answer: Due to catenation.

Question 13. Write the number of covalent bonds in CHr
Answer: Four

Question 14. Why unsaturated hydrocarbon gives a yellow flame with lots of black smoke when burnt in oxygen?
Answer: Due to incomplete combustion.

Question  15. What are the essential constituents of all organic compounds?
Answer: Carbon and hydrogen are the essential constituents of all organic compounds. However, carbon tetrachloride (CCl₄) is an exception

Question 16. What is the valency of carbon in its compounds?.
Answer: Carbon is tetravalent in its compounds.

Question 17. Draw the structural formula of methanoic acid. 
Answer:

Methanoic acid. 

Or HCOOH

Question 18. Carbon has four electrons in its valence shell. How does carbon attain stable electronic configuration?
Answer: Carbon is tetravalent because it has four valence electrons. To achieve noble gas configuration, it shares these electrons with four electrons of other atoms

The formula of citric acid is as follows: C₆H₈O₇

Question 19. State the name of-COOH functional group in citric acid.
Answer: Carboxylic acid

Question 20. Which of the following belongs to the same homologous series?
Answer: C₃H₆ and C₄H₈ belong to the same homologous series, which is alkenes with the general formula C_nH_2n

Question 21. Which has a triple bond; C₂H₄, C₃H_4, and C₃H₆?
Answer: C₃H₄ has a triple bond with the formula CH₃C ≡ CH.

Question 22. The molecular formula of butane is C₄H₁₀. What is the formula of butene?
Answer: The formula of butene is C₄H₈.

Question 23. A compound with the molecular formula C₃H₆O is used as a fuel. Identify the compound.
Answer: The compound is ethanol with formula C₂H₅OH.

Question 24. Write the names of the next homologous of CH₃CH₂OH and HCOOH.
Answer: Propanol and ethanoic acid, respectively.

Question 25. Give a test to identify the presence of ethanoic acid.
Answer: Dip a strip of blue litmus paper in the solution of ethanoic acid. Its colour will change to red.

Question 26. Out of butter and groundnut oil, which is unsaturated?
Answer: Groundnut oil is unsaturated.

Question 27. Write the molecular formula of alcohol, which can be derived from butane.
Answer: CH₃—CH₂—CH₂—CH₂—OH (Butanol)

Question 28. Name the second member of the alkyne family. Give its structure.
Answer: The second member of the alkyne family is propyne. Its structural formula is

Question 29. List two characteristic features of carbon which when put together rise to several carbon compounds.
Answer:

1. Catenation
2. Tetravalent

Question 30. The molecular formula of’A’ is C₁₀H₁₈ and B’ is C₁₈H₃₆ Name the homologous series to which they belong.
Answer: ‘A’ belongs to alkyne and ‘B’ belongs to alkene.

Question 31. How did ethanoic acid get its name as glacial acetic acid?
Answer: The melting point of ethanoic acid is 290K, and hence it often freezes during winter and forms ice-like flakes.

Question 32. Why are carbon and its compounds used as fuel for most applications
Answer: Carbon and its compounds are used as a fuel because when they are burnt, they give a large amount of energy in the form of heat

Question 33. Intake of small quantities of methanol can be lethal. Comment.
Answer:

Methanol is oxidized to methanal in the liver. Methanal reacts rapidly with the components of cells. It causes the protoplasm to coagulate. It also affects the optic nerve, causing blindness.

Question 34. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability concatenation of the two elements. Give reasons.
Answer:

Carbon exhibits catenation much more than silicon or any other element due to its smaller size, which makes the C-C bonds strong while the Si-Si bonds are comparatively weaker due to their large size.

Question 35. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
Answer: The two can be distinguished by subjecting them to the flame. Saturated hydrocarbons generally give a clear flame, while unsaturated hydrocarbons give a yellow flame with lots of black smoke.

Question 36. Which of the following hydrocarbons undergo additional reactions: C₂H₆, C₃H₈, C₃H₆, C₂H_2, and CH₄.
Answer: Unsaturated hydrocarbons undergo additional reactions. The following are the Unsaturated hydrocarbons among the given examples: C₃H₆ and C₂H₂.

Question 37. Which organic compound is added to make ethanol unfit for drinking purposes?  What is the name of the mixture formed?
Answer:  Methanol which is highly poisonous methanol is added in small amounts to ethanol to make it unfit for drinking purposes. The mixture is called methylated spirit or denatured alcohol.

Question 38. List two characteristics of covalent compounds.
Answer: Covalent compounds have low melting and boiling points. Covalent compounds do not conduct electricity.

Question 39. How will you convert ethene into ethanol? Give the chemical reaction involved.
Answer: Ethene is converted into ethanol by passing its vapours through water in the presence of sulphuric acid. This reaction is called the hydration of ethene.

Question 40. What is a homologous series? Which two of the following organic compounds belong to the homologous series? ,C₂H₆,C₂H₆O,C₂H₆O₂,CH₆O
Answer: For the definition of homologous series, consult the text part. The compounds CH₄O and C₂H₆O belong to the same homologous series known as alkanols.

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Definitions

1. Carbon:

Carbon is tetravalent and easily forms a large variety of compounds on combination with carbon and other atoms by sharing ofelectrons. It exhibits the phenomenon of allotropy, i.e., exists in two or more forms in the same state

For example: Graphite and diamond.

2. Covalent bond:

When two atoms achieve stability by sharing an electron pair, each contributes one electron to the electron pair. In this way, the atoms can be regarded as having acquired a noble gas configuration.

3. Covalent compounds:

Some atoms share electrons among themselves or with other atoms to attain a stable octet configuration. Bonds formed are covalent bonds and the compounds so formed are covalent compounds. Depending on the number of shared pair ofelectrons, there is a single covalent bond, a double covalent bond, or a triple covalent bond.

These compounds have low melting points and boiling points. They do not dissolve in water, do not conduct electricity, and are directional.

4. Catenation: Catenation is the property of carbon to get attached to other carbon atoms. Up to 60 carbon atoms are found to get attached in the shape of a ball (Fullerenes).

5. Allotropy:

When an element possesses two or more different forms in the same state, they are called allotropes and the phenomenon is known as allotropy. For example, diamond and graphite are the two allotropes of carbon.

6. Fullerenes: Fullerenes are allotropes of carbon.

For example: Buckminsterfullerene is an allotrope of carbon with 60 carbon atoms arranged in the shape of a football.

7. Hydrocarbons: Hydrocarbon Compounds containing only carbon and hydrogen are called hydrocarbons.

8. Saturated hydrocarbons: Compounds of carbon and hydrogen attached in chains, branches, or rings, by single covalent bonds

For example: Alkanes (CnH_2n+2): methane (CH₄), ethane (C₂H₅), propane (C₃H₈), and butane (C₄H₁₀).

9. Unsaturated hydrocarbons:

Unsaturated hydrocarbons are compounds of carbon and hydrogen with either a carbon-carbon double bond (C ≡ C) or a carbon-carbon triple bond (C = C) in their molecules.

For example: Alkenes (C_nH₂), ethene (C₂H₄), propene (C₃H₆), butene (C4Hg). Alkynes (C_nH_32n-2): ethyne (C₂H₂), propyne (C₃H₄) and butyne (C₄H₆).

10. Functional groups:

Groups that determine the chemical nature of an organic compound. In a hydrocarbon, one or more hydrogen atoms are replaced by another element or group. These confer specific properties to the compound regardless of the length and nature chain and hence are called functional groups.

11. Alkyl radical: The group formed by removing the hydrogen atom from an alkane molecule is called an alkyl radical or group.

12. Functional group: A group that determines the chemical nature of a compound is called a functional group.

13. A homologous: A homologous series is a group or family of compounds that contain the same functional group but have different chain lengths. In their molecular formulae, two successive homologs differ by one carbon and two hydrogen atoms.

14. Isomerism: In carbon compounds, different compounds are formed with different structures but with the same molecular formula.

These compounds are called isomers and the phenomenon is called isomerism.

For example: Butane(C₄H₁₀)can be written as:

15. Nomenclature of carbon compounds:

1. Identify the number of carbon atoms in the main chain. For example, methane, ethane, propane, and butane for one, two, three, four carbon atoms, etc.
2. The name of the functional group can be given either a prefix or a suffix (see table below).
3. If the functional group is used as a suffix, the e- of hydrocarbon is substituted by a suffix.
4. The carbon atoms are numbered from the side of the functional group.

16. Fatty acid:

Carboxylic acids containing long chains of carbon atoms are fatty acids. They are used as mild acids in foods, cold drinks, drugs, and perfumes and are chief constituents of washing soap.

17. Chemical properties of carbon compounds:

Carbon and its compounds burn in oxygen with liberation of heat and light. Saturated hydrocarbons burn with a blue flame and unsaturated with a yellow flame.

18. Addition reactions: Unsaturated hydrocarbons add up hydrogen or halogens

⇒ \(\underset{\text { Ethene }}{\mathrm{CH}_2}=\mathrm{CH}_2+\mathrm{Br}_2 \longrightarrow \underset{\text { 1, 2-Dibromoethane }}{\mathrm{CH}_2 \mathrm{Br}-\mathrm{CH}_2 \mathrm{Br}}\)

19.  Substitution reactions: In the presence of light, halogens are substituted with hydrogen in saturated hydrocarbons

20. Ethanol: Ethanol is produced on a large scale by the fermentation of sugar or starch with enzymes (invertase and zymase) present in the yeast.

1. It reacts vigorously with sodium with the evolution of H₂
2. It can be dehydrated at 443 K with excess concentrated sulphuric acid.

21. Esterification: Reaction in which alcohol combines with carboxylic acid in the presence of concentrated sulphuric acid.

It gives ethanal (acetaldehyde) in the presence of mild oxidizing agents like cupric oxide (Cu₂O) and acetic acid in the presence of acidified potassium dichromate.

21. Enzymes: Enzymes are catalysts, which bring about biochemical changes.

For example:  Lactose enzyme turns milk-sugar, lactose into lactic acid.

22. Denatured alcohol: To make alcohol unfit for drinking, it is mixed with poisonous substances like methanol, pyridine, and blue dyes.

23. Ethanoic acid gets neutralized by bases like sodium hydroxide, and sodium carbonate to give sodium acetate salt.

24. Soaps:

Soaps are sodium or potassium salts of chain carboxylic acid molecules, in which two ends have different properties, one is hydrophilic (dissolves in water), while the other end is hydrophobic (dissolves in hydrocarbons). When cleansing clothes, the hydrophobic part attaches to dirt (oily) and the hydrophilic part attaches to water which on washing pulls away the hydrophobic part along with dirt.

25. Detergents:  Detergents are similar to soaps buthydrocarbonpart here is obtained from p

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Short Question And Answers

Question 1. What would be the electron dot structure of carbon dioxide which has the formula CO₂ The electron-dot formula of CO₂ is given as:
Answer:

Question 2. What would be the electron dot structure ofa molecule of sulfur which is made up of eight atoms of sulfur?
Answer:

The electron-dot structure of sulfur is made of eight atoms of sulfur in a ring as shown.

Question 3. How many structural isomers can you draw for pentane?
Answer:

Three structural isomers can be drawn for pentane:

Question 4. What are the properties of carbon which lead to the huge number of carbon compounds we see around us?
Answer:

Two properties of carbon which lead to the huge number of carbon compounds are:

1. Tetravalency
2. Catenation

Question 5. What will be the formula and electron dot structure of cyclopentane?
Answer:

The formula of cyclopentane will be C₅H₁₀ Its electron-dot structure is written as

Question 6. Draw the structure for the following compounds

1. Ethanoic acid
2. Bromopentane
3. Butanone
4. Hexanal

Answer:

Question 7. How can ethanol and ethanoic acid be differentiated based on their physical and chemical properties?

Question 8.  Explain the formation of sum when hard water is treated with soap.
Answer:

Hard water contains soluble salts of sulfates and chlorides of calcium and magnesium. When soap is used to clean using hard water, calcium and magnesium present in hard water produce an insoluble substance called scum that remains after washing the cloth with water.

Question 9. What is hydrogenation? What is its industrial application?
Answer:

The addition of hydrogen to an unsaturated hydrocarbon in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons is called hydrogenation. The process is used to make healthy vegetable oils in industry.

Question 10. What is the difference between two consecutive members in a homologous series of alkanes in terms of:

1. Molecular mass.
2. Number of atoms of elements.

Answer:

Difference in: Molecular mass = 14u Number of atoms = CH₂

Question 11. State the valency ofeach carbon atom in

1. An alkane and
2. An alkyne.

Answer:

1. The valency of a carbon atom in an alkane is four.
2. The valency of carbon atoms in an alkyne is four

Question 12. Write the molecular formula of benzene and state the number of double bonds in its structure.
Answer:

1. The molecular formula of benzene is C₆H₆.
2. It contains three double bonds in its structure.

Question 13. Which of these has the minimum number of carbon atoms? Answer:

1. Unsaturated hydrocarbons with double bonds.
2. Compound ‘C’ has a minimum number of carbon atoms.

Question 14. Why are alkanes regarded as saturated hydrocarbons while alkenes and alkynes as unsaturated hydrocarbons?
Answer:

Alkanes contain C—C bonds in the molecules and a normal tetrahedral bond angle of 109°. 28′ is not disturbed. On the other hand, both alkenes and alkynes have multiple bonds (>C = C< or – C ≡ C – bond). The tetrahedral bond angle is no longer present. These are under strain and therefore, unsaturated.

Question 15. A compound ‘X has the molecular formula C₃H₆O with the structural formula CH₃CH₂CHO. Give its IUPAC name. Can another compound have the same molecular formula? Give the structure and IUPAC name of that compound also.
Answer:

The IUPAC name of X’ is: Propanal. Another compound Y can also have the same molecular formula but a different structural formula. It is propanone.

The compounds X and Y are related to each other as functional isomers.

Question 16. What happens when- (Give equations also).

1. Methane reacts with excess chlorine in the presence of diffused sunlight.
2. Ethanol undergoes combustion.

Answer:

Question 17. List four characteristics of homologous series.
Answer:

1. Same functional group.
2. Similar chemical properties.
3. Successive member differ by- CH₂unit/14u./
4. Gradation in physical properties.

Question 18.

1. Draw the structures of the following compounds

1. Ethanoic acid
2. Butanone

2. Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction?
Answer:

1.

2. When ethanol (C₂H₅OH) changes to ethanoic acid (CH₃COOH):

• There is a decrease in the number of hydrogen atoms by two.
• There is an increase in the number of oxygen atoms by one.

2. Therefore, the conversion represents an oxidation reaction.

Question 19.

1. What are esters? How are they formed? 
2. Write two uses of esters.

Answer:

1. Esters are the group of organic compounds that contain the functional group(—COOR) called the ester group.  The value of R may change as -CH₃, -C₂H₅, -C₃H₇, etc.

A few examples of esters are:

Esters are formed as a result of a chemical reaction called esterification.

2. Uses of esters

• Esters have a pleasant smell. These are used as flavoring agents and also in perfumes.
• Esters of glycerol known as triglycerides, are used in the manufacture of soaps.
• This reaction is called the saponification reaction.

Question 20. State the meaning of the functional group in a carbon compound. Write the functional group present in Ethanol and Ethanoic acid and also draw their structures.
Answer:

An atom or group of atoms that determine the chemical properties of organic compounds is called a functional group. They confer specific properties to the compound, regardless of the  length and nature of the carbon chain

Question 21.

1. Distinguish between saturated hydrocarbon and unsaturated hydrocarbon with the help of the combustion process.
2. Write the chemical names of C₄H₁₀ and C₂H₂ and draw their structures.

Answer:

Question 22. Why vegetable oils are considered healthy as compared to vegetable ghee? How are vegetable oils converted into vegetable ghee? Name and define the process involved. Answer:

• Vegetable oils contain unsaturated fatty acids while vegetable ghee contains saturated fatty acids which are said to be harmful to health.
• Vegetable oils are converted into vegetable ghee by adding hydrogen in the presence of catalysts palladium (Pd) or nickel (Ni).
• The process involved in this is an addition reaction (hydrogenation).It is defined as the addition of hydrogen atoms in carbon atoms of an organic compound.

Question 23. Give the electron dot structure and structural formula of the first member of the alkene and alkyne families Answer:

Question 24. How will you convert ethene into ethanol? Give the chemical reaction involved.
Answer:

Ethene is converted into ethanol by passing its vapors through water in the presence of sulphuric acid. This reaction is called the hydration of ethane

Question 25. What happens when:

1. Ethanol is burnt in the air and
2. It is oxidized? Write the corresponding reactions involved.

Answer: 1. Ethanol produces carbon dioxide, water, and energy when it is burnt in the air CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + Energy 2. Ethanol is oxidized into ethanoic acid

Question 26. Why are detergents preferred over soaps for washing clothes in hard water? Explain
Answer:

Detergents are preferred over soaps for washing clothes in hard water because:

1. They do not form insoluble precipitates with calcium and magnesium ions in hard water.
2. They give more lather in hard water.
3. They have strong cleansing action.

Question 27. What happens when ethyl alcohol and acetic acid react with each other in the presence of cone H₂SO₄
Answer:

When C₂H₅OH reacts with CH₃COOH, i.e., ethanol with ethanoic acid, a sweet-smelling ester is formed.

Question 28. State two characteristic features of carbon which when put together give rise to a large number of carbon compounds.
Answer:

The size of the carbon atom is very small (Atomic radius bonds = 77 pm) The strength of the C-C bond is quite high (355 kJ mol^-1) Therefore, any number of carbon atoms can be linked by covalent bonds. This self-linking property is called catenation.

Question 29. Why are some compounds saturated while others are unsaturated? 
Answer:

The compounds in which all the four valences of carbon are satisfied by hydrogen atoms are saturated in nature while the compounds in which the required number of hydrogen atoms are not available are unsaturated.

For example:

Question 30. Write the name and molecular formula ofan organic compound having its name suffixed with ‘-ol’ and having two carbon atoms in the molecule. With the help of a balanced chemical equation indicate what happens when it is heated with an excess of one. H₂SO₄
Answer:

The compound is ethanol and its molecular formula is C₂H₅OH. Upon heating with an excess of the cone. H₂SO₄ loses a molecule of H₂O and forms ethene. The reaction is known as the dehydration reaction.

Question 31. Explain with the help of chemical equations, the following properties of carbon.

1. Combustion
2. Oxidation

Answer:

1. Combustion:

C₂H₅OH + 3O₂→ 2CO₂ + 3H₂O

2. Oxidation

Question 32. Name an element, other than carbon which exhibits the property of catenation upto seven or eight atoms’? Are these compounds stable?
Answer:

The element is silicon (Si). It also belongs to group 14. It also shows catenation but its size is more than that of carbon, and the Si-Si bond is comparatively weak. Though upto seven to eight atoms can be linked to form different compounds, the stability of these compounds decreases gradually.

Question 33. Write the structure of

1. Hexanal
2. But-2-ene

Answer:

Question 34. How will you name the following compounds?

Answer:

1. Ethanal
2. Ethanol
3. Methanal
4. Chloroethane

Question 35. The molecular formula C₂H₆O can represent an aldehyde as well as a ketone. Write their structures and name them. How are they related to each other? 
Answer:

The aldehyde and ketone with formula C₂H₆O are propanal and propanone. Having the same molecular formula, these are isomers. As the functional groups are different, these are regarded as functional isomers.

For example:

Question 36. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur write the chemical equation giving the name of the reactants and the product of such a reaction.

Answer:

1. Alkanes. General formula: C_nH_2n+2

2. Conditions: Presence of catalysts such as Palladium or Nickel.

3. Equations:

Question 37. Draw the electron-dot structure for ethyne. A mixture ofethyne and oxygen is burnt for welding. In your opinion, why cannot we use a mixture of ethyne and air for this purpose?

Answer: In pure oxygen, ethyne undergoes complete combustion, and a high temperature suitable for welding is attained.

Whereas air contains less percentage/amount of oxygen which results in incomplete combustion of ethyne and the temperature required for welding is not attained.

Question 38. What is meant by a homologous series of carbon compounds? Classify the following carbon compounds into two homologous series and name them. 

1. C₃H₄
2. C₃H₆
3. C₄H₆
4. C₄H₈
5. C₅H₈
6. C₅H₁₀

Answer: A group of organic compounds having the same functional group and similar structures in which the successive members differ by CH₂ group. C₃H₄, C₄H₆, C₅H₈ : Alkyne C₃H₆,C₄H₈, C₅H₁₀ , Alkenes

Question 39. Why does micelle formation take place when soap is added to water? Will a micelle be formed in all types of solvents? Justify your answer.
Answer:

When soap is added to water, micelle formation takes place. This is because the hydrocarbon chains of soap molecules are hydrophobic while the ionic ends are hydrophilic and hence soluble in water. Micelle will not form in all types of solvents. It will form in such type of solvent where soap is insoluble in that particular solvent.

Question 40. Carbon does not from ionic compounds. Why?
Answer:

To form ionic bonds carbon either should lose 4^e+ or gain 4^e- to form C⁴⁺ or C^-4-ion. Losing 4^e+ needs a large amount of energy and by gaining 4^e-, it will have 10^e-. It is difficult for 6 protons to hold 10e^–. So C⁴⁺ and C^4- is not possible.

Question 41. What are soaps? Why do they form scum with hard water?
Answer:

1. Soaps are sodium or potassium salts of higher fatty acids.
2. The soluble Ca and Mg salts present in hard water react with soap to give insoluble salts to produce scum.

Question 42. Write the names ofthe following compounds

Answer:

1. Pentanoic acid
2. Butyne
3. Heptanal
4. Pentanol

Question 43. Identify and name the functional groups present in the following compounds

.

Answer:

Question 44. A compound X is formed by the reaction ofa carboxylic acid and alcohol in the presence ofa few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO4 followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of

1. Carboxylic acid
2. Alcohol and 
3. The compound X.

Also, write the reaction.

Answer:

1. Carboxylic acid is ethanoic acid
2. Alcohol is ethanol
3. X is ethyl ethanoate

Question 45. A gas is evolved when ethanol reacts with sodium. Name the gas that evolved and also write the balanced chemical equation ofthe reaction involved.
Answer:

The gas that evolved is hydrogen.

The reaction is as follows:

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

Question 46. Carbon, a Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with

1. Chlorine (Group 17 of Periodic Table)
2. Oxygen (Group 16 of the periodic Table)

Answer: Carbon tetrachloride (CCl₄) Carbon dioxide (CO₂)

Question 47. In electron dot structure, the valence shell electrons are represented by crosses or dots.

1. The atomic number of chlorine is 17. Write its electronic configuration.
2. Draw the electron dot structure of the chlorine molecule.

Answer:

1. K =2 ,L = 8 , M = 7

2.  Chlorine

Question 48. Match the reactions given in Column (A) with the names given in column (B)

Answer: 1- D,2- A,3- B,4-C

Question 49. A compound having molecular formula C₂H₆O is a saturated hydrocarbon and is a very good solvent. How can you convert it into unsaturated hydrocarbon?IdentifyXand shows its conversion with the help of the equation.
Answer:

‘X’is CH₃—CH₂OH (ethanol). It can be made unsaturated by heating it with a cone. H₂SO₄ which is a dehydrating agent that removes water from it, thereby forming ethene.

Question 50. Ethene is formed when ethanol at 443 K is heated with excess ofconcentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.
Answer:

Sulphuric acid acts as a dehydrating agent.

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Multiple Choice Questions

Question 1. Carbon exists in the atmosphere in the form of

1. Carbon monoxide only
2. Carbon monoxide in traces and carbon dioxide
3. Carbon dioxide only
4. Coal

Answer: 3. Carbon dioxide only

Question 2. Which of the following statements is usually correct for carbon compounds?

1. These are good conductors of electricity

2. These are poor conductors of electricity

3. These have strong forces of attraction between their molecules

4. These do not have strong forces of attraction between their molecules

1. 1 and 3
2. 2 and 3
3. 1 and 4
4. 2 and 4

Answer: 4.  2 and 4

Question 3. A molecule of ammonia (NH₃) has

1. Only single bonds
2. only double bonds
3. Only triple bonds
4. Two double bonds and one single bond

Answer: 1. Only single bonds

Question 4. Buckminsterfullerene is an allotropic form of

1. Phosphorus
2. Sulfur
3. Carbon
4. Tin

Answer: 3.  Carbon

Question 5. Which of the following are the correct structural isomers of butane?

Answer: 1

Question 6.

In the above-given reaction, alkaline KmnO₄ acts as

1. Reducing agent
2. Oxidizing agent
3. Catalyst
4. Dehydrating agent

Answer: 2. Oxidizing agent

Question 7. Oils treated with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of

1. Addition reaction
2. Substitution reaction
3. Displacement reaction
4. Oxidation reaction

Answer: 1. Addition reaction

Question 8. In which ofthe following compounds, —OH is the functional group?

1. Butanone
2. Butanol
3. Butanoic acid
4. Butanal

Answer: 2. Butanol

Question 9. The soap molecule has a

1. A hydrophilic head and a hydrophobic tail
2. A hydrophobic head and a hydrophilic tail
3. A hydrophobic head and a hydrophobic tail
4. A hydrophilic head and a hydrophilic tail

Answer: 1. A hydrophilic head and a hydrophobic tail

Question 10. Which ofthe following is the correct representation of the electron dot structure of nitrogen?

Answer: 4

Question 11. The structural formula of ethyne is

Answer: 1

Question 12. Identify the unsaturated compounds from the following

1. Propane

2. Propene

3. Propyne

4. Chloropropane

1. 1 and 2
2. 2 and 4
3. 3 and 4
4. 2 and 3

Answer: 4. 2 and 3

Question 13. Chlorine reacts with saturated hydrocarbons at room temperature in the

1. Absence of sunlight
2. Presence of sunlight
3. Presence of water
4. Presence of hydrochloric acid

Answer: 2.  Presence of sunlight

Question 14. In the soap micelles

1. The ionic end of soap is on the surface ofthe cluster while the carbon chain is in the interior ofthe cluster
2. The ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster
3. Both the ionic end and carbon chain are in the interior ofthe cluster
4. Both the ionic end and carbon chain are on the exterior ofthe cluster

Answer: 1. The ionic end of soap is on the surface ofthe cluster while the carbon chain is in the interior ofthe cluster

Question 15. Pentane has the molecular formula C₅H₁₂. It has

1. 5 covalent bonds
2. 12 covalent bonds
3. 16 covalent bonds
4. 17 covalent bonds

Answer: 3. 16 covalent bonds

Question 16. The structural formula of benzene is

Answer: 3

Question 17. Ethanol reacts with sodium and forms two products. These are

1. Sodium ethanoate and hydrogen
2. Sodium ethanoate and oxygen
3. Sodium ethoxide and hydrogen
4. Sodium ethoxide and oxygen

Answer: 3. Sodium ethoxide and hydrogen

Question 18.  The correct structural formula of butanoic acid is

Answer: 4

Question 19. Vinegar is a solution of

1. 50%- 60% acetic acid in alcohol
2. 5%- 8% acetic acid in alcohol
3. 5%- 8% acetic acid in water
4. 50%- 60% acetic acid in water

Answer: 3.  5%- 8% acetic acid in water

Question 20. Mineral acids are stronger acids than carboxylic acids because

1. Mineral acids are completely ionised

2. Carboxylic acids are completely ionised

3. Mineral acids are partially ionised

4. Carboxylic acids are partially ionised

1. 1 and 4
2. 2 and 3
3. 1 and 2
4. 3 and 4

Answer: 1.  1 and 4

Question 21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms,

Example: Hydrogen. After the formation of four bonds, carbon attains the electronic configuration of

1. Helium
2. Neon
3. Argon
4. Krypton

Answer: 2. Neon

Question 22. The correct electron dot structure ofa water molecule is

Answer: 3

Question 23. Which of the following is not a straight-chain hydrocarbon?

Answer: 4

Question 24. Which among the following are unsaturated hydrocarbons?

1. 1 and 3
2. 2 and 3
3. 2 and 4
4. 3 and 4

Answer: 3. 2 and 4

Question 25. Which ofthe following does not belong to the same homologous series?

1. CH
2. C₂H₆
3. C₂H₆
4. C₄H₈

Answer: 4. C₄H₈

Question 26. The name ofthe compound CH₃—CH₂—CHO is

1. Propanal
2. Propane
3. Ethanol
4. Ethanal

Answer: 1.  Propanal

Question 27. The heteroatoms present in CH₃—CH₃—O—CH₂—CH₂ Cl are

1. Oxygen

2. Carbon

3. Hydrogen

4. Chlorine

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1 and 4

Answer: 1. 1 and 2

Question 28. Which of the following represents the saponification reaction?

Answer: 4

Question 29. The first member of the alkyne homologous series is

1. Ethyne
2. Ethene
3. Propyne
4. Methane

Answer: 1.  Ethyne

Question 30. Ethane, with the molecular formula C₂H₆ has

1. 6 covalent bonds
2. 7 covalent bonds
3. 8 covalent bonds
4. 9 covalent bonds

Answer: 2. 7 covalent bonds

Question 31. Butanone is, a four-carbon the functional compound

1. Carboxylic acid.
2. Aldehyde
3. Ketone
4. Alcohol.

Answer: 3. Ketone

Question 32. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

1. The food is not cooked completely.
2. The fuel is not burning completely.
3. The fuel is wet.
4. The fuel is burning completely.

Answer:  2. The fuel is not burning completely.

Air Around Us

Air Around Us Properties Of Air

Some of the properties of air are given below.

• Air is invisible, and it can only be felt.
• It occupies space.
• It is colorless, odourless, and transparent.
• It takes the shape and odor of the object or place where
• It is present in.
• It is a mixture of different gases and another particle

Presence Of Air

Atmosphere

The thin layer of air surrounding the Earth is called the atmosphere. This thin layer extends up to many kilometers above the surface of the Earth. It filters out harmful radiations and other particles entering into the Earth’s atmosphere.

We know that mountaineers carry oxygen cylinders with them while climbing high mountains. This is necessary because the amount fair reduces as we move higher in the atmosphere. At higher altitudes, the level of oxygen is very low creating breathing problems

Science Insight:

A thin layer of ozone is present in the upper atmosphere. It protects the Earth by blocking harmful rays coming from the Sun.

Read and Learn More Class 6 Science Notes

Composition Of Air

Air is a mixture of many gases. The major components of air are nitrogen (78%) and oxygen (21%). The remaining 1% contains carbon dioxide, water vapor, argon and a few other gases, along with dust and smoke. The composition of dust and smoke varies from time to time and place to place

Let s study these components of air in detail

1. Water Vapour

It is the water present in gaseous form in the air and can be formed through the process of evaporation.

• This is why when air comes in contact with cool surfaces, these vapors condense into drops of water,
• Example:  Appearance of water drops on the surface of a glass containing ice during summer. Water vapor in air is important for the water cycle in nature.

2. Oxygen

• It is an essential component present in the air. Survival of all living beings on land and in water is because of oxygen.
• It is a vital part in the respiration process in all living beings, and also a supporter of burning.
• It does not burn but is required in the burning of a substance or a fuel.

Presence of Oxygen in Water and Soil:

• Animals and plants living in water are aquatic organisms. These organisms use oxygen, which is dissolved in water for breathing.
• Those organisms which live in soil and plants (through their roots) use the air present in between the space of soil particles.

3. Nitrogen

It is a major component of air. It is required by both plants and animals for their growth, but they are not able to absorb the nitrogen directly from the air. Nitrogen is first converted to nitrate only, then plants absorb it from the soil. Animals absorb it by consuming food prepared by plants. Unlike oxygen, nitrogen does not support burning.

4. Carbon Dioxide (CO₂)

It is also an essential component of air like oxygen that makes a small composition in the air plants consume carbon dioxide while making their food by the process of photosynthesis.

• On the other hand, we take in oxygen and give out carbon dioxide during respiration. Burning of plant and animal matter also uses oxygen, and in turn, carbon dioxide is given out.
• We feel suffocated if we burn something in a closed room. This is due to the excess of CO₂ present in the room. So, it is advisable not to burn dry leaves and discarded remains of the crop, which causes pollution.
• It does not support burning and can be used as a fire extinguisher to put off the fire.

5. Dust and Smoke

The burning of fossil fuels produces smoke. It contains few gases and fine dust particles which are harmful to living organisms.

• Long chimneys could be seen in factories. It takes the smoke and dust particles away from our noses, but in turn, it is harmful to birds flying up in the sky.
• Dust particles are always present in the air in winter, we observe a beam of sunlight that filters through the trees.
• In which dust particles appear to dance merrily. Fine hair and mucus present inside the nose prevent the dust particles when we breathe.

Why do traffic policemen wear masks?

The traffic policemen who regulate traffic at a crowded city road crossing often wear masks. The traffic policemen wear masks to protect themselves from the smoke containing harmful gases which are emitted by the vehicles moving around them.

Replacement Of Oxygen In Atmosphere

All living organisms consume oxygen present in the air. The process of respiration by plants and animals uses oxygen present in the air. It is constantly replaced by plants through the process of photosynthesis.

• In this process, plants make their food, and oxygen is produced. Plants also consume oxygen for respiration, but they produce more of it than they consume.
• That is why, we say, plants produce oxygen.
• Animals cannot live without plants. The balance of oxygen and carbon dioxide in the atmosphere is maintained through respiration and photosynthesis. This shows the interdependence of plants and animals.

Uses of Air

We have seen how valuable the resource of air is. All of its components are vital for life on Earth.

Here, some uses of air are given below:

• It exerts pressure on objects that come in its way.
• It regulates temperature.
• Wind is used to rotate windmills. It is used for various purposes like drainage water from tube wells, running flour mills, generating electricity, etc.
• It is used by living organisms for breathing.
• It is used to inflate the tires of vehicles.
• It is used for the winnowing process.
• It helps in the traveling of sound and smell as when air moves, it carries sound and smell to a distance
• It helps in the movements of sailing yachts, gliders, parachutes, and airplanes. Birds and insects can fly due to the presence of air.
• It also helps in the dispersal of seeds and pollen of flowers of several plants.
• It plays an important role in the water, nitrogen, and oxygen cycle.

Activity 1

Aim:

To show the presence of air with the help of a firkin.

Materials Required:

Paper, stick, scissors, etc.

Procedure:

1. Make a firki by using a paper strip.
2. Hold the stick of the firki and move it in different directions.

Observation: 

We will observe that the firki starts rotating. The firki moves/rotates when the air strikes its blades.

Conclusion:

We conclude that air is present around us

Activity 2

Aim:

To show that air occupies space using an empty bottle.

Materials Required:

Empty glass bottle, container, filled with water etc.

Procedure:

• Take an empty glass bottle.
• Now, hold the bottle in an inverted position (with its open mouth facing downwards) in a container filled with water.
• Observe if water enters the bottle.
• Now, tilt the bottle in water and observe it.

Observation:

• The water does not enter into the inverted glass bottle.
• In tilted glass bottle. Air present in the bottle goes out in the form of air bubbles. As the air from the ott e pes, water starts entering the glass bottle and occupies the place of air.

Conclusion:

We conclude that the glass bottle which appears to be empty is filled with air.

Activity 3

Aim:

To demonstrate the presence of oxygen in air which supports burning.

Materials Required:

2 candles, matchbox, 2 glass

Procedure:

• In the presence of your teacher, fix two small candles of the same size. Light both the candles.
• Cover one of the candles with an inverted glass and observe

observation:

It is observed that the candle covered with a glass tumbler was extinguished after some time whereas the other candle continued burning

Conclusion:

We concluded that air contains some amount of oxygen and it supports burning

Activity 4

Aim:

To show the presence of dust particles in the air.

Materials Required:

Black curtains or black chart papers.

Procedure:

• Find a room in a school/home.
• Close all the doors and windows with the help of black chart paper or black curtains.
• Make a small hole in the black chart I have fixed on the window, facing the Sun, and observe.

Observing the presence of dust in the air with sunlight:

Observation:

• A thin beam of sunlight enters the room through the small hole made in the chart.
• We could see the tiny dust particles moving in the beam of light in the dark room.

Conclusion:

• We conclude that air also contains dust particles.
• The presence of dust particles in the air varies from time to time and from place to place.

Activity 5

Aim:

To show the presence of dissolved air in water.

Materials Required:

Tumbler/beaker, water, tripod stand, burner.

Procedure:

• Take a number/beaker filled with water and keep it on a tripod stand
• Heat the water slowly by using a burner.

Observation:

Before the water begins to boil, tiny bubbles appear on the inner surface of the tumbler/beaker. These bubbles are of air dissolved in water.

Conclusion:

We conclude that water contains dissolved air and when it is warmed, air comes out in the form of bubbles

Activity 6

Aim:

To show that soil contains trapped air.

Materials Required:

Small jar, water, soil.

Procedure:

• We take a small jar filled with water.
• Add a handful of soil into the jar and observe the changes that occur.

Observation:

While adding the soil into the jar, air bubbles observed which are formed in water. This shows that the soil contains some air trapped in between its soil particles.

Conclusion:

We conclude that soil contains trapped air, which helps the organisms to survive that live inside the soil. Also, the roots of plants respire by using this air.

Fun With Magnets

Fun With Magnets Magnet

The substances having the property of attracting iron are known as magnets. In our daily life observations, we have often seen certain stickers on the doors of refrigerators. The white iron boards in schools often have dusters that can be stuck to them. A pin holder has lots of pins stuck to it and a crane picking up pieces of iron from waste, etc All these objects have a special substance called a magnet in them. Nowadays, magnets are used to make mobile devices, telephones, televisions, etc

Picking up pieces of Iron from waste:

Some common Items that have magnets Inside them:

Discovery of Magnet

• The magnet was discovered accidentally. There was a shepherd named Magnes who lived in ancient Greece. He used to take his herd of sheep and goats to the nearby mountains for grazing. He would take a stick with him to control his herd. The stick had a small piece of iron attached at one end.
• One day, he was surprised to observe that he had to pull hard to free his stick from a rock where he used to go with his sheep and goats. It seemed as if the stick was being attracted by the rock
• The rock was a natural magnet that attracted the iron tip of his stick. So, after the name of a shepherd, the rock was named as magnetite and magnetite contains iron.
• Some people believe that magnetite was first discovered at a place called Magnesia

Read and Learn More Class 6 Science Notes

Natural Magnet and Artificial Magnet

• The magnet that is found in nature is known as natural magnet,
• Example: Magnetite and lodestone, whereas the magnet that can be made by magnetising materials like iron, cobalt, nickel, etc., is known as an artificial magnet or man-made magnet.
• Nowadays, artificial magnets are prepared in different shapes, e.g. bar magnet, horse-shoe magnet, cylindrical or ball-ended magnet

Magnetic and Non-Magnetic Materials

• All the materials are not attracted by magnets. Magnets attract only certain materials. The substances which get attracted by the magnet are called magnetic materials,
  • Examples: Iron, steel, nickel, and cobalt.
• While those substances which are not attracted by the magnet are called non-magnetic materials,
  • Examples:  Rubber, plastic, stainless steel, feather, and leather.
• We can see this in daily life observation,
  • Example:  When a needle slips from our hand on the floor. To find it, a magnet. Since a needle is made of iron, it can be attracted by a magnet

Note: Non-magnetic materials cannot be magnetised. It means that non-magnetic materials cannot be converted into magnet

Poles of Magnet

• When we bring a magnet close to iron filings, we see that iron filings get attracted toward a magnet. If we observe, we will find that most of the iron filings stick at the two free ends of a magnet. These free ends are called the poles of a magnet. Poles of the magnet are the regions of strongest magnetism.
• All magnets have two poles north pole and south pole, whatever their shape may be. Usually, north (N) and south (S) poles are marked on the magnets.
• The north pole and south pole of a magnet can’t exist independently or cannot be separated. If a magnet is broken into two or more pieces, each of them will have a north pole and south pole

Finding Direction

• An interesting property of a magnet is that a freely suspended bar magnet always comes to rest in a north-south direction.
• The end ofthe magnet that points towards the north is called the north-seeking end or north pole of the magnet and the other end that points towards the south is called south seeking end or south pole of the magnet
• In early centuries, t is property of magnets was very useful for travelers. They used to suspend magnets with a thread to find directions.

Using the Sun for Finding Directions

• By using the direction of the rising sun in the morning, we can find out the rough direction towards the east. If we stand facing east, then our left will be north.
• It may not be very exact but it will help to make out all the directions as

Compass

A compass is usually a small box with a glass cover on it. A magnetised needle is pivoted inside the box, which can rotate freely. It has a dial with directions marked on it as shown in the figure

Science Insight:

Earth also behaves like a giant magnet. The magnetic compass lines up with the earth’s magnetic poles such that the north pole of the magnetic needle always points to the earth’s north pole and vice-versa.

To find the directions using a compass

The compass is placed at a place where we wish to know the direction. The compass needle points in the north-south direction, when it comes to rest. The dial of the compass is rotated and aligned with the north-south axis of the needle. This gives the north-south direction.

Make Your Magnet

There are several ways to make a magnet from a magnetic material. One of the simplest ways to make a magnet is given below.

• First of all, take an iron bar, which is to be made of a magnet, and keep it on the wooden table.
• Now, take a bar magnet and try to hold it with one end with your hand.
• Keep the other end in touch with the one end of the bar.
• Now, move the magnet toward the other end of the iron bar.
• Now, lift the magnet at the end and place it at the end from where you have started.
• Repeat this process about 30-40 times.
• Bring a pin or some iron filings near the iron bar to check whether it has become a magnet. If not continue the process for some more time.
• Remember that the pole of the magnet and the directions of its movement should not change.

Attraction And Repulsion Between Magnets

• When north-north or south-south poles of two magnets come close, then they repel each other, i.e., it can be stated that like poles repel each other
• On the other hand, when the north-south or south-north poles of two magnets come closer, then they attract each other, i.e. it can be stated that unlike poles attract each other.
• The attractive or repulsive force that is exerted between the poles of a magnet is also known as a magnetic force.

Science Insight:

Maglev train works on the principle of attraction and repulsion between magnets. In this, one set of magnets is used to repel and push the train up off the track and another set is used to move the elevated train ahead

A Few Cautions for Magnet

There are some ways to keep magnets safe

• Magnets lose their properties if they are heated, hammered, or dropped from some height.
• Magnets also become weak, if they are not stored properly.
• To keep them safe, bar magnets should be kept in pairs with their unlike poles on the same side.
• Keep magnets away from cassettes, mobiles, television, music systems, CDs, and computers.
• They must be separated by a piece of wood while two pieces of soft iron should be placed across their ends.

Activity 1

Aim:  To observe the effect of a magnet.

Material Required:  A magnet, a paper cover, a cup, a thread stand, and a metal clip

Procedure:

• Take a paper cup and fix it on a stand with the help of a clamp
• Place a magnet inside the cup and cover it with paper, so that the magnet is not visible.
• Attach a thread to a clip made of iron and fix the other end ofthe thread at the base ofthe stand
  (remember to keep the length of the thread sufficiently short).
• Bring the clip near the base of the cup. The clip will rise in the air without support

Conclusion:  We have concluded that a magnet is a substance that has the property to attract iron.

Activity 2

Aim:

To identify magnetic and non-magnetic materials using a magnet

Material Required:

A magnet, different types of materials Material Required A magnet, different types of materials

Procedure:

• Hold a magnet and bring it close to each one of these materials.
• Observe which materials get attracted towards the magnet.
• Prepare a table of those materials that are attracted by a magnet.

Conclusion:

We have concluded that objects which are made of iron, copper, etc. (magnetic materials), are attracted by magnets. On the other hand, objects which are made of plastic, paper, cloth, etc. (non-magnetic materials), are not attracted by a magnet

Activity 3

Aim: To identify the amount of iron particles in the soil of different areas

Material Required: A magnet, samples of the soil from a different area

Procedure:

• Rub a magnet In the sand or soil. You will observe some particles of soil stick to the magnet.
• Gently shake the magnet to remove the particles of soil.
• You will observe some particles still stick to It. These might be small iron pieces.

Prepare a table for different samples of soil:

Conclusion:  We have concluded that different areas have different amounts of iron particles in their soil

Activity 4

Aim:  To observe that the magnetic strength is maximum at the poles.

Material Required:  A magnet, and some iron filings.

Procedure:

• Take some iron filings on a paper sheet.
• Put a magnet on the sheet and smoothly roll it on the iron filings
• Wait for a few seconds, we will find that the maximum number of iron filings are attracted at the end of get and a very smaller amount at the center

Conclusion: We have concluded that the magnetic strength of the magnet is maximum at the poles.

Activity 5

Aim:

To show the directive property of a magnet. Material Required A magnet, a wooden stand, and a thread.

Procedure:

• Hang the magnet with the thread freely in the air. When it comes to rest, mark two points on the ground to show the position of the ends of the magnet.
• Rotate the magnet by gently pushing one end in any direction and when it comes to rest, mark the position of the ends of a magnet.
• Repeat the above step, and the magnet always comes to rest in the same direction, i.e. north-south direction.
• Repeat this activity with an iron bar, a plastic, or a wooden scale. You will find that the observation is different for every step.

Conclusion: 

We have concluded that a magnet has directive properties. It is always directed to the north-south direction

Activity 6

Aim: To make a simple magnetic compass. Do opposite poles attract each other?

Material Required: A cork, a magnetised needle, and a water bowl.

Procedure:

• Insert the magnetised needle through a small piece of cork.
• Let the cork float in water in a bowl. Make sure that the needle does not touch the water.
• Note the direction in which the needle points.
• Rotate the cork, with the needle fixed in it in different directions.
• Note the direction again in which the needle points.
• You will find that the needle always points in the same direction.

Conclusion:

We have concluded that magnetized needle always comes at rest in the north-south direction of the earth.

Activity 7

Aim: To observe attraction and repulsion between magnets.

Material Required: Magnets, toy cars.

Procedure:

• Take two small toy cars and label them A and B.
• Place a bar magnet on top ofeach car along its length and fix them with rubber bands such that, in car A, the south pole of the magnet is towards its front, and in car B, die north pole of the magnet is towards its front.
• Place both cars close to one another. You will find that the cars are moving towards each other.
• Now, place the cars close to each other such that the rear side of car A faces the front side of car B. You will find the cars are moving away from each other.
• Repeat this activity by changing the position of the car and observing it.

Positions of the car:

Conclusion: 

We have concluded that like poles repel each other and unlike poles attract each other.

Electricity And Circuits

Electricity And Circuits Electric Cell

An electric cell is a device that produces electricity from chemicals stored inside it A device that is used to produce a small amount of electricity by chemical reactions is known as an electric cell.

• There is a wide utilization of these cells such as in alarm clocks, wristwatches, cameras, and many other devices.
• The electric cell produces electricity till the whole of its chemical gets used. When the chemicals inside the cell are exhausted, the cell needs to be replaced by a new one.

Structure of Electric Cell

A common electric cell is a cylindrical cell as shown in

• A metal cap on the upper side, a positive terminal (+)•
• A metal disc on the lower side, a negative terminal (-)
• The chemicals ammonium chloride and zinc chloride present inside between the two terminals are called electrolytes.

Read and Learn More Class 6 Science Notes

Note:  Terminal is a point at which either current starts or reaches finally after flowing.

• For current to flow, the positive terminal must be connected to the negative terminal and this polarity must be maintained.
• An electric cell is a single unit but when several electric cells are used together, it is called a battery, which can be used to power bigger devices.

Why should you never connect the positive (+) and negative (-) terminals of the cell directly?

Never join the two terminals of the electric cell without connecting them through a switch and a device like a bulb. If you do so, the chemicals in the electric cell get used up very fast and the cell stops working.

Electric Bulb

A bulb is a device that converts electrical energy into light and heat energy. The electric bulb was invented by Thomas Alva Edison in 1879.

An electrical bulb has the following parts:

1. A glass bulb.
2. A thin coil of wire inside the glass bulb is called a filament. A bulb glows when an electric current passes through its filament. The filament heats up and glows to give light, filament is made of tungsten material.
3. It has two thick wires that provide support to the filament. One wire is connected to the metal case and the other wire is connected to the metal tip.
4. The metal tip and the metal case act as two terminals of an electric bulb.

These two terminals do not touch each other and are separated by an insulating material

Electric Circuit

A closed path along which the electricity can flow is called an electric circuit. It provides a complete path for electricity to pass (current flow) between two terminals of the electric cell

Electric current always flows from the positive to the negative terminal of the cell. The current passes only when the circuit is complete.

Types of circuits are as follows

• Closed Circuit:  It is an unbroken path through
  which electricity can pass easily. It is a circuit in
• Open Circuit:  It is a broken path through which electricity cannot pass. It is a circuit in which there is a gap in the connections between the terminals of the cell, wires the bulb, etc

Science Insight

Electric circuits can be classified as series and parallel circuits. In a series circuit, the electric current is the same, but in a parallel circuit, the current may vary. Electric circuits in our home are parallel circuits so that each appliance can take current as per it requirement

Fused Bulb

• A bulb is said to be fused when the filament of a bulb is broken due to overheating.
• A break in the filament of an electric bulb means a break in the path of the current between the terminals of the electric cell. Therefore, no current passes through its filament, and a fused bulb does not glow.

Electric Switch

A simple device -which is used to either break the electric circuit or to complete it, is known as an electric switch or key. The switches used in lighting of electric bulbs and other devices in homes

Electric, which can be used as a lamp. It has two or more two cells, one bulb, and a switch. When the electricity supply fails at home, a torch is used to provide light.

Electric Conductors And Insulators

Electric conductors are those materials that allow electric current to pass through them. c.g. Iron, silver, aluminum, copper, brass, graphite. On the other hand, insulators are those materials that do not conduct electricity and are resistive to the flow of current.

Examples: Rubber, plastic, wood, ceramic, porcelain, asbestos, glass, mica, cotton, jute, thermocol, wax, etc.

All metals are good conductors of electricity, while all non-metals (except carbon) are bad conductors of electricity. Silver is a better conductor of electricity than copper.

Science Insight:

Water conductor or insulator?

Water behaves as both a conductor and an insulator. If water has impurities that help in conducting electricity, then it behaves like a conductor. On the other hand, if we use distilled water where no impurities are present, it behaves like an insulator.

Importance of Conductors and Insulators

• Conductors and insulators are equally important to us.
• Switches, electrical plugs, and sockets are made of conductors.
• On the other hand, insulators like rubber and plastic are used for covering electrical wires, plugs, tops, switches, and other parts of electrical appliances that people might touch.

Note:  Your body is a conductor of electricity. Therefore, be careful when you handle an electrical appliance.

Activity 1

Aim:

To observe and study the working of torch bulbs.

Material Required:  A torch, and a magnifying glass.

Procedure

• Take a torch and look inside its bulb by magnifying glass. You can also take out the bulb with the help of a teacher.
• You will find a thin wire fixed in the middle of the glass bulb, as shown in the figure.
• Now, switch ON the torch and observe the part of the bulb which is glowing

Conclusion:

We have observed that the thin wire in an electric bulb that produces light is known as the filament of the bulb

Activity 2

Aim:

To demonstrate the right connection of bulb and cell.

Material Required:

Four colored wires, a cell, and a bulb.

Procedure:

1. First, remove the plastic covering of each end of the wire.
2. Try to make connections as shown in the observation table.
3.  Observe, whether the bulb glows or not, in each connection

Observation Table

Conclusion

We have concluded from the above observation that (f) bulbs will glow because the circuit is complete and in other cases, bulbs will not glow because the circuit is incomplete

Activity 3

Aim:

To make a bulb light up using an electric cell.

Material Required:

A torch bulb, an electric cell, and a wire (with ends exposed or naked)

Procedure:

• Join one end of the electric wire around the base electric bulb and leave the other end free.
• Fix the tip of the base of the torch bulb with the positive terminal of the electric cell.
• Bring the tip of the free end of the electric wire in contact with the negative terminal of the electric cell. We will find that the torch bulb starts glowing.
• Remove the electric bulb away from the positive terminal of the electric cell. We notice that the bulb stops glowing.

Homemade torch:

Conclusion:

We have noticed that the bulb will glow’ when the circuit is complete but when we remove the bulb from the metal cap, the circuit is incomplete and the bulb goes off

Activity 4

Aim: To make a simple electric switch.

Material Required:

Two drawing pins, a safety pin, electric wires, a bulb, an electric cell, and a piece of thermal.

Procedure:

• Insert a drawing pin into the ring at one end of the safety pin and fix it on the thermal.
• Now, fix the other drawing pin on the thermal sheet in a way that the free end of the safety pin can touch it and attach the piece of wire with the drawing pins.
• Make a circuit by connecting an electric cell and a bulb with the switch.
• Rotate the safety pin, so that its free end touches the other drawing pin. You will find that the bulb starts glowing.
• Now, move the safety pin away from the drawing pin.

You will find that the bulb stops glowing

Conclusion:

• We have concluded that, when we touch the free end of the safety pin with the other drawing pin, then the switch is said to be ON. Thus, the bulb starts glowing.
• The bulb does not glow when the safety pin Is not in touch with the other drawing pin

Activity 5

Aim:

To examine whether a given material is a conductor or an insulator.

Material Required:

Key, scale, pins, glass bangle, electric bulb, electric cell, conducting wire.

Procedure:

• Make a conduction tester by connecting an electric cell and bulb with the help of wires
• Collect samples of different types of materials such assets, keys, scales, pins, etc.
• Join the free ends of the wires of your tester with two ends of the samples.

Now make a table of whether the bulb is glowing or not:

Conclusion:

We have concluded that objects which allow the current to pass through them are conductors, and objects which do not allow the current to pass through them are insulators.

Light Shadows And Reflections

Light Shadows And Reflections Luminous And Non-Luminous Objects

1. Luminous objects:

Luminous objects are those objects which give out or emit their light,

Example: Torch, bulb, the sun, stars, etc.

2. Non-luminous:

Non-luminous objects are those objects which do not emit their light and are visible to us when light from luminous objects falls on them and then reaches our eyes.

Example: Chair, moon, painting, etc.

Science Insight:

Moon and planets do not have their light, they reflect the light coming from the sun. So, they are non-luminous objects

Read and Learn More Class 6 Science Notes

Transparent, Opaque And Translucent Objects

The objects which allow us to see through them are called transparent objects.

• In other words, transparent objects are those objects that allow the light to pass through them completely. e.g. Glass, water, air, etc
• The objects which do not allow us to see through them are called opaque objects.
• In other words, opaque objects are those objects which do not allow the light to pass through them.
  • Example: Brick wall, cardboard, book, notebook, etc.
• The objects which allow us to see partially through them are called translucent objects.
• In other words, translucent objects are those objects which partially allow the light to pass through them.

Examples: Butter paper, wax paper, greased paper, etc.

Shadows

The dark patches formed by opaque objects behind them when they come in the path of light are called shadows.

Shadows are formed behind the opaque objects as they do not allow the light to pass through them. Shadows are formed only by opaque objects.

• Shadows of animals and birds hidden in your hand
• Shadow gives us some information about the shapes of objects.
• Sometimes, it can also mislead us because the shape of the shadow is not exactly that of the object.
• In our daily life observations, we have noticed that the criss-cross pattern due to the light coming from window grills is the shadow of grills.

Shadows:

To form a shadow, we need three things:

1. A source of light
2. An opaque object which comes in the path of light
3. A screen on which shadow forms

Science Insight:

The shadow can be seen screen. Grounds, walls of a room, etc., act as observed shadows in daily life.

Some Important Facts about Shadow

• The shadow of an object is formed on the opposite side of the light source.
• Shadow changes its lengths and direction during the day
• As the object moves, its shadow also moves.
• Shadows are always black irrespective of the colour of the object.
• The size and position of the shadow change with a change in the position of the light source or a change in the position of opaque objects

Pinhole Camera

A pinhole camera:

A pinhole camera is a simple device, which is used to obtain an image of a bright object on a screen. A pinhole camera is just a closed box with a tiny hole (pinhole) at one end and a translucent butter paper (screen) on the other end.

The light comes through the pinhole and the image is formed on butter paper (screen).

A pinhole camera works on the principle that light travels in a straight line.

The image formed by a pinhole camera is inverted and usually smaller in size as compared to the original object.

Never Ever Look Directly at The Sun:

An eclipse can be seen using a pinhole camera. When the eclipse is viewed through a pinhole camera, the sun’s image gradually becomes darker as the eclipse starts. We must take a precaution, i.e. not to see eclipse directly with our eyes as it may harm us.

Properties of Image Formed by Pinhole Camera

The image formed in a pinhole camera has the following characteristics

• The image in a pinhole camera is inverted (upside down) as compared to the object.
• The image in a pinhole camera is real (because it can be formed on a screen).
• The image in a pinhole camera is of the same colour as the object.
• The image in a pinhole camera can be smaller than the object, equational to the object or bigger than the object (depending on the distance of the screen from the pinhole).

Get it Right:

Students are often confused between mirror images and pinhole images. The image formed by a plane mirror is the same size as the object but the size of the image formed by a pinhole camera depends on the distance of the pinhole from the screen

Natural Pinhole Camera

• One of the interesting pinhole cameras in nature is the small holes formed by a large number of leaves under the tree.
• When we pass through under such trees, small circular patches seem to be under the tree. These circular patches are pinhole images of the sun.
• The gaps between the leaves act as the pinholes. These gaps are all kinds of irregular shapes but we can see circular images of the sun.

Why image of the sun is not inverted in a pinhole camera?

In our daily life observation, we observe upside-down images of people with a pinhole camera but we can’t see this type of image in the case of the Sun. The reason behind this is the symmetrical and spherical shape of the Sun. The image of the sun is inverted but due to symmetry, the image appears to be the same as that of the original

Light Moves in a Straight Line

When we see a candle through a straight pipe, then it is visible but if we see the candle through a bent pipe, then it is not possible to see it

This concludes the light travels in a straight line, so we can say that the formation of pinhole images and shadows is possible only, when light moves in a straight path.

Mirror And Reflection

A mirror is a smooth surface that sends back all the light falling on it. The phenomenon of sending the back of the light by the mirror or other smooth surface is called reflection. Any surface that is well-polished or shiny acts like a mirror.

Science Insight:

The mirror reflects the light at the same angle at which it hits the surface of the mirror. When we look into the mirror, we see our face inside it. The face we see Inside the mirror is the reflection of our face

We also see reflections of other objects that are in front of the mirror. Sometimes, we see reflections of trees, buildings and other objects in a pond or lake.

Reflection of tree In a pond:

Reflection of the face in a mirror:

Activity 1

Aim:

To classify the object is opaque, transparent or translucent.

Materials Required:

An eraser, plastic scale, pen, pencil, notebook, a single sheet of paper, tracing paper or a piece of doth, glass, etc.

Procedure

• Hold each object one by one.
• Try to look at something far away, through each object.
• Observe and make a table, whether you can see through the object or not and classify the object according to the observation.

Observing Objects that do Or do not allow light to pass through them:

Conclusion:

Through this activity, we have concluded that

• Transparent objects like glass, allow the light to pass through them completely. So, we can see objects through it very clearly.
• Opaque objects like pencils and notebooks do not allow light to pass through them. So, we cannot see the object through it.

1. Translucent objects like plastic scales partially allow the light to pass through them, So, we can sec objects through It but not clearly.

Activity 2

Aim:

To identify the opaque objects through its shadow.

Materials Required:

Different opaque objects like flowers, tables, chairs, kites, bulbs, sunlight, and some paper sheets.

Procedure

• Spread the paper sheets on the ground, so it acts as a screen.
• One by one hold each of the objects in the sunlight slightly above the ground and outline the shadows on the sheet.

Ask some other friends to identify the objects from these outlines of shadows.

Conclusion:

We have concluded from the above table that the shapes of shadow is not exactly those of the object, it can also mislead us about the object. So, we can’t always identify an object through its shadow

Activity 3

Aim:

To show that a screen is required for a shadow to be formed.

Materials Required:

A torch, an open ground, a paper sheet, etc.

Procedure:

• In the evening, take a torch and a large sheet of paper and go with your friends to an open ground.
• Direct the torch light towards the face of friend A.
• Observe if you can see any shadow behind him, you will probably not see any shadow.
• Now, ask friend B to hold a paper sheet behind friend A. This time, you will be able to see the shadow on the sheet.

Conclusion:

Conclusion  Through this activity, we have concluded that a shadow can be seen only when there is a screen behind an object.

Activity 4

Aim:

To know that shadow gives an accurate picture of the shape, size and colour of an object.

Materials Required: 

Some opaque objects like balls, tables, chairs, books, etc., and sheets of paper.

Procedure

• Firstly spread the paper sheets on the ground under sunlight.
• Hold the flower In the sunlight and observe the shape of the shadow formed on the paper sheet.
• Similarly, hold the colour balls one by one In the sunlight and observe the colour of shadows formed on the paper sheet.
• Similarly, hold the bottle at different angles and observe the length of shadows formed

Conclusion:

• Through step 2, we have concluded that some objects look similar to the shadows but some look very different.
• Through step 3, we have concluded that we cannot the colour of objects through shadows because shadows are always black.
• Through step 4, we have concluded that at different angles sizes of shadows are different.

So, finally, we can say that shadow cannot give the accurate shape, size and colour of the object.

Activity 5

Aim:

To make your pinhole camera.

Materials Required:

Two boxes, of tracing paper.

Procedure:

• Take two boxes such that one can slide into another with no gap in between them.
• Cut open one side ofeach box and on the opposite face ofthe larger box, make a small hole in the middle.
• In the smaller box, cut out a square from the middle with a side of about 5 to 6 cm and cover this open square in the box with tracing paper
• Slide the smaller box inside the larger one with the hole, in such a way that the side with the tracing paper is inside.
• Now, your pinhole camera is ready for use.
• Move the smaller box forward or backwards till you get a picture on the tracing paper pasted at the other end.

Conclusion:

We have concluded the following observations

1. Pinhole images are inverted images of the object

2. The size of the image decreases as we decrease the distance between the screen and the pinhole.

3. The size of the image increases as we increase the distance between the screen and the pinhole.

Activity 6

Aim:  To show that light travels in a straight line.

Materials Required:  A rubber tube or pipe and a candle.

Procedure

• Take a rubber tube or a pipe and fix a burning candle on the table.
• Try to see the flame of the candle through the hole in the pipe, you will be able to see it.
• Now bend this pipe a little and again try to see the flame of the candle through the pipe, you will not be able to see it.

Conclusion:

We have concluded that light travels in a straight line and cannot pass through a curved line.

Activity 7

Aim:

To show that the mirror changes the direction of light that falls on it

Materials Required:

A mirror, a source of light.

Procedure:

1. This activity involves three people and has to be done in a dark room or at night.

• The first person holds the torch and stands in a corner.
• The second person holds a mirror and stands at an angle.
• A third person stands away from both people.

2. Now direct a small beam of light on the mirror; A patch of light will appear on the other side of the room.

3. Adjust the torch in such a way that the patch of light falls on the third person in the room.

Conclusion:

We have concluded that the light is getting reflected by the mirror and the mirror can change the direction of the light beam falling on it.

Activity 8

Aim: 

To show that light travels in a straight line and gets reflected from a mirror.

Material required:

A torch, comb, mirror, a cardboard box and sheets.

Procedure:

• Fix a comb and a plane mirror on a cardboard box
• Spread the sheet of coloured paper at the base.
• Switch ON the torch and observe the beam of light falling on the mirror and getting reflected on paper.’

Conclusion:

We have concluded that light rays travel in a straight line and bounce off at the same angle from the mirror

Motion And Measurement Of Distances

Motion And Measurement Of Distances Story Of Transport

A way to carry people and goods from one place to another is called transport. We will now discuss how people traveled and carried goods from one place to another in earlier times and how they do it these days.

• In ancient times, people did not have any means of transport. They used to move only on foot and carry goods on their back. Later on, they began to use animals for transportation.
• For transport through water routes, boats were used from ancient times. Boats were simple logs of wood in which a hollow cavity could be made. Later, people learned to put together different pieces of wood and gave shapes to the boats. These shapes imitated the shapes of the animals living in water.
• After many years, man invented the wheel, which led to the discovery of wooden carts and sleds that helped man to transport goods on land and ice. Later, they used animals like horses and camels to pull the wheels. The invention of the wheel also led to the discovery of the bicycle.
• In the beginning of the 19th century, the invention of the steam engine introduced a new source of power to run transport vehicles.

Read and Learn More Class 6 Science Notes

Steam engines (which used coal as fuel for making steam) were used to pull trains on railroads (railway tracks) for carrying people and goods from one place to another. Steam engines were also used to run ships in the beginning.

Science insight:

James Watt (a Scottish engineer) invented the steam engine in 1756. The steam engine is called an external combustion engine because the fuel ; (coal) for making steam was burnt outside the engine.

• After a few years, the invention of the internal combustion engine (which uses petrol or diesel as fuel) gave us transport vehicles, which are known as automobiles (cars, buses, scooters etc.) for travel on land.
• On the other hand, motorized boats and ships were developed as means of transport on water.
• In the early years of 1900, aeroplanes were discovered as a means of transport which are also considered as the fastest means of transportation for goods and people.
• Electric trains, monorails, supersonic airplanes and spacecraft are also some of the 20th-century contributions to the modes of transport.

Need of Measurement

There are so many occasions when we come across a need to measure distance and length, e.g.,

• If you want to go to your friend’s house or the market, the first thing you want to know is the distance between your house and the place.
• The tailor needs to measure the length of the cloth to know if it is enough to stitch a kurta.

So, we can say that distance or length is the measure of how far or long something is. In other words, the actual path length covered by an object between two points is called distance.

Measurement

Measurement is the. method of comparison of any unknown quantity with a known quantity. This known quantity is known as a unit.

• The result of measurement is expressed in two parts, i.e. a number and a unit of the measurement.
• For example, we measured the length of the desk as 2 meters. In this case, the first part is a number that is 2 and the second one is a unit that is a metre.

Ancient Methods of Measurement

In ancient times, people used the following different units for the measurement of length and distance.

1. Handspan

Hand span is the length between the tip of the thumb and the little finger of our hand when we stretch it as shown in the figure.

2. Cubit

Cubit is the length between the tip of the middle finger and the elbow when we stretch our hand horizontally. It was used to measure length in ancient Egypt.

3. Yard

Yard is the length between the tip of the middle finger and the chin of an outstretched arm. It was used to measure the length of clothes and wires.

4. Footstep

The footstep is the length between the thumb and the heel of the foot. We used this method to measure the distance.

5.  Mutthi

Mutthi  (Fist) refers to the quantity that a person’s fist (mutthi) can hold. It was used to measure quantities of small things like wheat, rice sugar, etc.

6. Angul (finger)

Angul is the width of a finger. It was used to measure very small distances with the help of fingers. You may heard from your grandparents, it is the gap of chaar angul (four fingers).

Standard Units of Measurement

The ancient methods of measurement were inaccurate and changed from person to person. Hence, to have a fixed value for a unit of measurement, standard units of measurement were developed.

The standard system of units is called the SI system (System International and Units in French).

1. The SI unit for measuring length is a meter (m).

1 m = 100 cm, 1 cm = 10 mm

2. For long distances meter is not a convenient unit, hence we define a larger unit of length that is a kilometer (km).

1 km= 1000 m

3. The smallest unit to measure length is fermi (fm).

⇒ \(1 \mathrm{fm}=\frac{1}{10^{15}} \mathrm{~m}\)

Correct Measurement of Length

For measurement, usage of the correct device is very important,

Example:

You cannot measure the girth of a tree or the size of your chest using a meter scale. For this, measuring tape is more suitable. So, for measurement, usage of the correct device and way of measuring things plays a vital role.

1. Precautions while Taking Measurements:

For taking measurements, we must take care of the following things

1. To take measurements of the length of the object, we must put the scale along its length as shown in the figures.

2. If the end of the scale is broken and we are not able to see a zero mark, then take any full mark and subtract the reading of this mark from the reading at the other end as shown in the figures.

3. During measurement, the position of the eye is also very important. So, we must keep our eyes in such a way that it is exactly in front of the point where the measurement is to be taken as shown in the figure.

2. Measuring the Length of a Curved Line:

We cannot measure the length of a curved line directly by using a meter scale. We can use a thread to measure the length of a curved line. If we carefully move the thread along the curved line while keeping it stretched tightly and then measure the used part of the thread by a meter scale, we can get to know the length of the curved line.

Moving Things Around Us

When a body changes its position concerning time, then it is said to be in motion, e.g. moving ant, the hands of the clock, a running car, the revolution of the earth around the sun, etc.
On the other hand, when a body does not change its position concerning time, then it is said to be stationary or at rest.

Example: Table, house, tree, etc.

Types of Motion

• When we see around us, we experience the motion of a vehicle, the march past of soldiers, the running fan the motion of a bicycle, etc.
• Different objects show different types of motion. Some of the circular motion is periodic but a periodic motion may or the important types of motions stated as follows may not be circular

1. Rectilinear Motion:

A body is said to be in rectilinear motion, if it moves in a straight line without changing its direction of motion, e.g. Vehicle running on a straight road, the motion of a bullet when fired, sprinters in a 100 m race, march-past of soldiers, etc.

2. Circular Motion:

A body is said to be in a circular motion if it moves in a circular path around a fixed point,

Example:  Hands of a clock, the motion of a stone in the following figure. In this case, the distance of the stone from your hand is not changing because the length of the string is not changing.

3. Periodic Motion:

The motion which repeats itself after a regular interval of time is known as periodic motion,

Example: The motion of the minute hand of our wristwatch, the motion of a simple pendulum, revolution of planet around the sun.

Note You might have observed some objects possess more than one type of motion, e.g. sewing machine remains at rest while its wheels move in circular motion and the needle moves in periodic motion.

Activity 1

Aim:

To measure the length and width of the classroom by foot

Material Required:

Classroom and 3 friends.

Procedure:

• Place your foot along the length of the classroom.
• Now, put your second foot next to your first foot without leaving any space between the two feet.
•  Now, put your first foot next to your second foot
• Repeat this process until you reach the other side of the floor.
• Similarly, measure the width of the classroom. If some part remains to be measured as it is smaller than your foot, then use a string to measure that part of the length.
• Ask your friends to do the same procedure.

Now, make an observation flow chart as follows:

Conclusion:

Length and breadth are not the same, it varies from person to person.

Activity 2

Aim:

To measure the width of the table with a handspan to know about the unit.

Material Required:

A classroom table and 3 friends.

Procedure:

• Place your thumb on the left corner of the table as shown in the figure. Now, measure the complete width of the desk using your handspan.
• Count the number of handspans
• Now, ask your friends to do the same.

Record all the observations in a flow chart as shown below:

Conclusion Handspan is a known quantity and the width of the table is an unknown quantity. The measurement of the width of the table is different for different people.

Activity 3

Aim:

To measure the height of your friend using a handspan and then by using a meter scale.

Material Required:

1 marker, 1-meter scale and 3 friends.

Procedure:

• Ask one of your friends to stand with his back against a wall
• Make a mark exactly above your friend’s head.
• Measure the distance of this mark from the floor using handspan and then with a meter scale

Ask other friends to do the same flow chart:

• Now, record all the observations in a table as shown below Conclusion Height in handspan is different for different students because the length of their handspan is different.
• Height in cm is approximately the same. It varies slightly due to errors while marking.

Activity 4

Aim:

To measure the length of a curved line using thread.

Material Required:

A thread, a marker and a meter scale.

Procedure:

• Put a knot on the thread near one of its ends.
• Place this knot on the point A. Now, place a small portion of the thread along the curved line. Place a finger on the thread to hold it there.
• Using the other hand, stretch the thread a little more
• Repeat this process till the other end 2 and mark on a thread where it touches point 2.
• Now, stretch the thread along a meter scale and measure the length between the know and the final marker

Conclusion:

The length of the curved line from point A to point B is 10.2 cm.

Activity 5

Aim: 

To identify objects in motion and objects at rest.

Material Required: 

3-4 blank papers and pen

Procedure:

• Go to different rooms of your house and make a list of different objects that you see.
• Now, visit any nearby park and make a list of objects that you see.
• Now, visit any nearby market and again make a list.
• Now, divide all the objects into two parts.
• The first part is objects at rest and the second part is objects in motion.

Crowd Park:

Observation of the flow chart:

Conclusion:

From this activity, we concluded that some objects change their position like flying birds, balls, etc., and these objects are in motion. Some other objects do not change their position e.g. table, bench, etc., these objects are at rest.

Activity 6

Aim:

To understand the meaning of motion by observing an ant.

Material Required:

Sugar cubes, a clear white paper of large size, and a gel pen.

Procedure:

• Visit your nearby garden and find a place where ants are present.
• Now, spread the white sheet near the ants and spread some sugar cubes on it.
• When any ant starts moving on the paper, make a small mark near its position.
• Keep marking its position after every few seconds as it moves along the paper.
• After some time, shake the paper to make it free from sugar and ants. Connect all the marked points with arrows to show the direction in which the ant moved.
• Conclusion From this activity, we concluded that the ant has changed its position after some time and the path of the ant is not definite.

Activity 7

Aim:

To observe the motion of a whirling stone.

Material Required:

A small stone and a strong string.

Procedure:

• Tie the stone with a string that you have.
• Now, hold the other end of the string.
• Now, whirl it with your hand and observe the motion of the stone. You will find that it is moving in a circular path.

Conclusion:

We concluded that the motion of the whirling stone is circular.