Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

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Class 8 : Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

The document Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes is a part of the Class 8 Course Science Class 8.
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Conduction of Electricity
Similar to many solids, some liquids also conduct electricity. Electrical conduction is the movement of electrically charged particles through a transmission medium. The movement can form an electric current in response to an electric field.

Conductor: Substances which allow electricity to pass through them are called conductors; such as silver, gold, acidic solution, salt solution, etc.

Insulator: Substances which do not allow electric current to pass through them are called insulators; such as plastic, rubber, etc.


Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes
Fig: Conduction of Electricity in Liquid


Good conductor and Bad Conductor
Substances which allow electric current to pass through them easily are called good conductors of electricity; such as silver, gold, aluminium, etc.

Some substances allows electric current to pass through them but in very little amount. Therefore, such substances called bad conductors of electricity, rather than being called as insulator.


Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

Fig: Electricity conductivity of good and bad conductor


In fact, most of the substances allow electric current to pass through them under certain conditions, so instead of using terms conductors and insulators, good conductors and bad conductors are used.


Testing of conduction of electricity through liquid
Liquids which contain salt dissolved in them conduct electricity. The conduction of electricity through a liquid can be tested using two electrodes and a bulb.

But the conduction of electricity through the liquids which are poor conductor cannot be tested. But conduction of electricity through such liquids can be tested using LED or magnetic compass needle.

For this, you need a compass needle, an empty matchbox, two electric cells, some wires, a plastic bottle cap and the liquid which is to be tested. Keep the compass needle inside the empty tray of matchbox and wrap a couple of rubber bands around it. Connect the wires to the battery and insert two wires in the liquid which is kept in the plastic bottle cap. You will observe that when the current flows through the wire, there is deflection in the compass needle. This shows that the given liquid conducts electricity. In fact, magnetic compass needle can detect even feeble current. LED can also be used in place of compass needle.

Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

Fig: Testing of conduction of electricity through liquid

Salts dissolved in water are responsible for conduction of electricity through water. Tap water, acid solutions, basic solutions, etc. are good conductors of electricity. Distilled water is poor conductor of electricity because in no salt is present in distilled water.

Chemical Effects of Electric Current
When electric current is passed through a conducting solution, some chemical reaction takes place.


Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

Fig: Chemical Effect of Electric current

Electrodes:
These are conducting materials through which current enters or leaves a substance.

Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes
Types of Electrodes:
(i) Positive Electrode: It is the electrode which is connected to the positive terminal of the battery. It is also known as Anode.
(ii) Negative Electrode: It is the electrode which is connected to the negative terminal of the battery. It is also known as Cathode.

Example:
(a) When electric current is passed through water, water dissociates into hydrogen and oxygen. Hydrogen is deposited over negative pole and oxygen is deposited over positive pole. Deposition of hydrogen and oxygen at different poles is visible in the form of bubbles.

(b) When electric current is passed through the solution of a metal salt, such as solution of copper sulphate, metal gets deposited at the negative pole, because metal is positively charged.

(c) Sometimes, the color of solution also changes when electric current passes through it.

The above examples are some of the chemical effects of electric current. The chemical reaction depends upon the type of solution through which electric current is passed.

Electroplating
Electroplating is one of the chemical effects of electric current. Electroplating is a chemical process using which a metal is coated with a layer of another desired metal. Electroplating is done to make the metals shiny. Electroplating is done over the articles made of iron to make the iron shiny and to prevent iron from getting rusted.


Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

Fig: Electroplating  Chemical Effect Current


Example: Wheel rims, handle of cycle, etc. are made shiny by the method of electroplating.
Process of Electroplating
In the process of electroplating, metal salt solution is taken in a container. Salt of metal is chosen which is to be coated over another metal. Metal which is to be coated is dipped in the solution and connected with negative pole. Metal for desired coating is connected with positive pole.

Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

Fig: Process of Electroplating

When electric current is passed through the solution, metal from anode is dissolved in the salt solution and deposited over the negative pole (cathode). Thus, coating of desired metal is obtained on another metal.

Use of electroplating
(a) Water pipes, which are made of iron, are coated with a layer of zinc metal by the process of electroplating. Zinc is less reactive than iron and thus prevents the iron pipe from getting rusted.

(b) Rims of wheel of cycle, cars, etc. are electroplated with chromium metal. Layer of chromium metal give them shiny appearance and prevents from rust.

(c) Ornaments made of silver or other cheap metals are electroplated with gold to give them appearance like gold.

(d) Tin cans used for storing food are made of iron electroplating with a coat of tin. Tin is less reactive than iron, and prevent foods packed in them from getting spoiled. 

(e) Electroplating is used to coat a metal object with a layer of a different metal.  


Chapter Notes Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes

Fig: Different Uses of Electroplating

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