CBSE Class 8 Science Chapter 11 Chemical Effects Of Electric Current Conduction Of Electricity In Liquids
Like solids, liquids may also conduct electricity. Some liquids are good conductors of electricity, and some are poor conductors of electricity.
To examine whether a liquid permits electric current to pass through it or not, we can use the tester. When the liquid like lemon juice, vinegar etc., is between the two ends of the tester, the bulb glows.
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On the other hand, when the liquid, like distilled water, is between the two ends of the tester, the bulb does not glow.
” Chemical Effects Of Electric Current Class 8 “
” Cbse Class 8 Science Chapter 11 Notes “
From the above experiments, we can say that lemon juice and vinegar are the liquids that allow electricity to pass through them.
i.e. They are conducting liquids, while distilled water does not allow the electricity to pass through it, i.e. it is not a conducting liquid.
CBSE Class 8 Science Chapter 11 Detecting Weak Electric Current Through A Liquid
In some situations, even if the liquid is conducting but the bulb does not glow.
It may be due to the low conductivity of the liquid that it allows only a weak current to pass through it. This weak current is not sufficient to heat the filament of the bulb to a high temperature.
If the electrical conductivity of liquid which we are testing, is very small, then the current in the circuit may be weak. The weak electric current flowing through liquids can be detected in two ways.
” Conduction Of Electricity In Liquids “
With the help of LED (Light Emitting Diode)
With the help of a compass surrounded by turns of circuit wire.
By using LED, LED can be used in the tester in place of a bulb. It lights up even when a very weak current passes through the circuit.
l.F.n has two wires, one wire is longer than the other. The longer wire is connected to the positive terminal, and the shorter wire is connected to the negative terminal of the battery.
” Electroplating Process Class 8 “
With the help of a compass We know that, electric current produces a magnetic effect. So, when a weak electric current flow’s in a wire, this produces a magnetic effect due to w’hich a compass needle starts deflecting. So, this test circuit shows the presence ofelectric current.
” Lemon Juice And Vinegar Conductivity “
Poor Conductors can be Good Conductors
Poor conductors are those materials which allow electricity to pass through them under certain conditions.
As we know, air is poor conductor of electricity but during lightning, an electric current pass through it. Similarly, distilled water does not conduct electricity but when we add some salts, acids, bases to it, this solution starts conducting electricity.
So, we can say that liquids like solutions of acids, bases and salts are good conductors ofelectricity. The water that we get from sources like handpumps, taps, tube wells, etc., contains a small amount of natural salts. These natural salts make it a good conductor of electricity.
CBSE Class 8 Science Chapter 11 Chemical Effects Of Electric Current
When electric current is passed through conducting liquids, it causes chemical changes in the liquids. This is called the chemical effect of electric current.
The passage of an electric current through a conducting solution may cause the following chemical effects
- Change in colour of the conducting liquid.
- Deposits of metal on the electrodes.
- Bubbles of gas near the electrodes.
Electrodes
The conducting rods are generally made up of carbon. These rods are known as electrodes.
The electrode connected to the positive terminal of the battery is called the anode, while the electrode connected to the negative terminal of the battery is called the cathode.
” Magnetic Needle Deflection Experiment “
The chemical effect produced by an electric current depends on the nature of the conducting solution and the nature of the electrode used.
When electric current is passed through conducting water, it breaks the water into hydrogen gas and oxygen gas.
This breaking of water through electric current is called chemical decomposition. Such chemical decomposition of conducting liquids through electric current is called electrolysis.
CBSE Class 8 Science Chapter 11 Electroplating
The process of depositing a thin layer of desired metal over a metal object with the help of electric current is called electroplating.
Example: Wheel rims, handle of a bicycle are made shiny by coating them with chromium metal. It is one of the most common applications of the chemical effects of electric current.
The objective of electroplating is
- To protect metal from rusting or corrosion.
- To make metal look shinier and attractive.
” Bulb Glowing In Circuits “
Note: Carbon is only a non-metal, which can be electroplated with copper.
Process Of Electroplating
- When an electric current is passed through the copper sulphate solution, the solution dissociates into copper and sulphate.
- Now, the free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it.
- An equal amount of copper gets dissolved into the solution from the other electrode (Copper plate).
- Hence, the loss of copper from the solution is restored and the process of transferring copper from one electrode to other, continues.
- Here, the copper transfers from anode to cathode.
” Distilled Water And Salt Solution “
Uses of Electroplating
Chromium has a shiny appearance, and it does not corrode and resists scratches. So, the objects made from a cheaper metal get a coating of chromium over them.
The following are the uses of electroplating in our day-to-day activities.
- The electroplating of silver and gold on the less expensive metals like iron, copper, etc is done by jewellery makers. So, these kind of ornaments have the appearance of silver or gold but arc much less expensive.
- Tin cans used for storing food are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, by electroplating the iron with tin, the food does not come into contact with iron directly, so it is protected from getting spoiled.
Some Major Concerns of Electroplating
The conducting solutions like copper sulphate in the electroplating process are the pollutants for environment. It contains various types of salts which may be poisonous.
It may affect aquatic as well as human life, so the disposal of the used conducting solution is a major concern for us.
Good Conductors: Materials which allow an electric current to pass through it is known as good conductors. Examples: Salt water.
Poor Conductor: Materials which allow only a very small amount of current to pass through them are known as poor conductors.
Examples: Acetic acid /vinegar.
Electrolyte: A liquid which conducts electricity is known as an electrolyte.
” Cbse Class 8 Science Notes “
Electrode: The carbon rods whose metal caps are covered by copper wires and joined to a battery are known as electrode.
Electrolytic cell: An arrangement in which a cell having two electrodes is kept in a conducting liquid in a vessel is called an electrolytic cell.
Electrolysis: The chemical decomposition produced by passing an electric current through an electrolyte is called electrolysis.
Electroplating: The process of depositing a thin layer of desired metal over a metal object with the help of electric current is called electroplating.