CBSE Class 10 Science Chapter 1 Chemical Reactions And Equations Very Short Answer Questions

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

Question 1. Out of rusting of iron or melting of iron, which one is a physical change?
Answer: Melting of iron

Question 2. In the electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?
Answer:

Because during electrolysis, water splits into two molecules of hydrogen and one molecule of oxygen.

2HO  → (Electrolysis )  → 2 H₂O

Question 3. Which one is a chemical change, electrolysis of water or Sodium chloride exposed to sunlight?
Answer: Electrolysis of water

Question 4. All decomposition reactions are endothermic reactions. Explain why?
Answer: Because energy in the form of heat, light or electricity is required for decomposition.

Question 5. What change in colour is observed when white silver chloride is left exposed to sunlight? State the type of chemical reaction in this change.
Answer:  Silver chloride becomes grey. It is a photochemical decomposition reaction.

Question 6. Balance the given chemical equation:

⇒ \(\mathrm{Fe}(\mathrm{s})+\mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(\mathrm{~s})+\mathrm{H}_2(\mathrm{~g})\)

Answer:

⇒ \(3 \mathrm{Fe}(\mathrm{s})+4 \mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(\mathrm{~s})+4 \mathrm{H}_2(\mathrm{~g})\)

Question 7. Balance the given chemical equation:
Answer: FeSO₄(s)   → (Heat) → Fe₂O₃(s) + SO₂(g) + SO₃(g)

Question 8. Balance the following chemical equation:

⇒ \(\mathrm{Fe}(s)+\mathrm{H}_2 \mathrm{O}(g) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(s)+\mathrm{H}_2(g)\)

Answer:

⇒  \(3 \mathrm{Fe}(s)+4 \mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(\mathrm{~s})+4 \mathrm{H}_2(g)\)

Question 9. What type of coating is formed on silver articles when they get corroded?
Answer: The silver articles form a black coating of silver sulphide (Ag₂S).

Question 10. On what basis is a chemical equation balanced?
Answer: It is based on the law of conservation of mass.

Question 11. Balance the given chemical equation:

Al(s) + CuCl₂(aq)→  AlCl₃(aq) + Cu(s)

Answer: 2Al(s) + 3CuCl₂(aq)→ 2AlCl₃(aq) + 3Cu(s)

Question 12. What type of coating is formed on copper articles when they get corroded?
Answer: The copper articles form a green coating of basic copper carbonate

Question 13. State one basic difference between a physical change and a chemical change.
Answer:

In a physical change, no new substance is formed whereas in a chemical change, a new substance is formed.

Question 14. On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green. Predict the new compound formed which imparts a blue-green colour to the solution.
Answer:

The new compound formed is copper (II) chloride (CuCl2) which imparts a blue-green colour to the solution.

Question 15. Name the oxidising and reducing agent in the following reaction: Cu + H₂O→Cu + H₂O
Answer:

The oxidising agent is CuO.

The reducing agent is H₂.

Question 16. What is meant by the skeletal equation?
Answer: An unbalanced chemical equation is called a skeletal equation.

Question 17. If copper metal is heated over a flame, it develops a coating. What is the colour and composition of this coating?
Answer: The colour of the coating is black and it is composed of CuO or copper oxide.

Question 18. Which one is a chemical change – Electrolysis of water or sodium chloride exposed to sunlight?
Answer: Electrolysis of water

Question 19. A magnesium ribbon should be cleaned before burning it in the air. Why?
Answer: It should be cleaned to remove the dust particles and the oxide that may be present on its upper surface so that it comes directly in contact with air.

Question 20. Which of the following is a chemical change?

1. Burning of wax
2. Melting of wax

Answer: 1. Burning of wax

Question 21. Why do gold and platinum not corrode in moist air?
Answer: They are least reactive and do not react with substances present in moist air.

Question 22. Why do potato chip manufacturers fill the packet of chips with nitrogen gas?
Answer: To provide an inert atmosphere to prevent chips from getting oxidised. N₂ does not allow chips to get spoiled by oxidation.

Question 23. How will you define a reducing agent?
Answer: A reducing agent is a substance which can lose electrons or which can add hydrogen or remove oxygen.

Question 25. Name the process in which the gain of electrons takes place.
Answer: Reduction is a process which involves the gain of electrons

Question 24. A white salt on heating decomposes to give brown fumes, and a residue is left behind. Name the salt.
Answer: Lead nitrate is white salt.

Question 25. Hydrogen is a highly inflammable gas and oxygen is a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
Answer:

This is because the properties of the compound (H₂O) are different from the properties of its constituting elements, i.e., H₂ and O₂.

Question 26.

• AgNO₃(aq) + NaCl(aq)→ AgCl(s) ↓ + NaNO₃(aq)
• FeS + H₂SO₄ →FeSO₄ + H₂S ↑

Consider the above-mentioned two chemical equations with two different kinds of arrows(↑ and ↓) along with products. What do these two different arrows indicate?
Answer:

↑ shows the gas evolved, whereas shows an insoluble substance (precipitate) formed.

Question 27. What is the colour of FeSO₄.7H₂O crystals? How does the colour change upon heating? Give a balanced chemical equation for the change. 
Answer:

FeSO₄. 7H₂O is green and loses water of crystallisation when it is heated. It is then decomposed to Fe₂O₃ (brown-coloured), SO₂ and SO₃

2FeSO₄(s) → Fe₂O₃(s)+  SO₂(g) + SO₃(g)

Question 28. Oil and fat-containing food items are flushed with nitrogen. Why?
Answer: To keep food items fresh and to save from the oxidising effect of oxygen, food items are flushed with nitrogen gas.

Question 29. Why do we store silver chloride in dark-coloured bottles?
Answer: Because silver chloride on exposure to sunlight undergoes dissociation.

Question 30. A boy has been collecting silver coins and copper coins. One day he observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings?
Answer: The phenomenon responsible for these coatings is corrosion.

Question 31. FeSO₄. 7H₂O, green colour crystals on heating changes colour. Why?
Answer:  The green colour of ferrous sulphate crystals is due to the presence of 7 water molecules (water of crystallisation).