Chemical Effects Of Electric Current - Class 8 Physics - Extra Questions

The process of depositing a layer of any desired metal on another material by means of electricity is called "electroplating". It is mostly applied to modify the surface features of an object. The process can also be used to build thickness.

For electroplating, the particle to be plated is made the cathode.

Examples of electroplated objects are as follows:
(i) Chromium plating is done on different parts of cars, buses and motor cycles to give them shiny appearance.
(ii) A fine layer of gold is deposited on the silver ornaments and they are called gold-plated ornaments.
(iii) Iron used in constructing a building is coated with a layer of zinc. This protects iron from corrosion and rusting.

Chromium plating is a technique in which the object is covered with a layer of chromium metal. This thin layer prevents the metal from corrosion and scratches. The metal is shiny in nature. So, the object which is covered with this layer appears shiny.

$$\bullet$$ Electroplating is an art of protecting metal surface from corrosion and giving it pleasant appearance.

Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.

The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of a gas may be formed on the electrodes. Deposits of metal may be seen on electrodes. Changes of colour of solutions may occur.

Chemical effect of electric current is used in electroplating. It is a process of depositing a layer of any desired metal on another material by means of electricity. 

The three effects of electric current are:
1. Heating effect
2. Magnetic effect
3. Chemical effect.

Electroplating is the process of depositing a layer of a metal on a metallic or non-metallic electrode by electrolysis in an electrolytic cell.
Let us take an iron spoon which is to be electroplated with copper.
For this, we take copper plate and iron spoon as electrodes and copper sulphate $$(CuSO_4)$$ is taken as an electrolyte. The electrodes are connected through an external circuit as shown in the figure.
On passing current through the electrolyte, it is decomposed into $$Cu^{+2}$$ and $$(SO_4)^{2-}$$ ions. As $$Cu^{+2}$$ ion is positively charged, it moves towards the negative terminal, i.e. iron spoon, and is deposited on it. Thus, iron spoon is plated with copper. There is no scarcity of $$Cu$$ atoms because the copper atoms go into the solution from the positive terminal, i.e. copper plate. This process called electroplating continues until the iron spoon is coated with copper.

Take copper sulphate solution in a glass through. Dip a carbon rod in the solution. Use it as the cathode, i.e. connect it to the negative terminal of the battery. Take a pure copper strip, dip it in the solution and use it as anode, i.e. connect it to the positive terminal. Pass electricity through the solution by closing the circuit. The positively charged copper ions from the solution will move towards the carbon rod which is acting as the cathode. The copper ions that are positively charged get attracted towards the negative electrode, the carbon rod get deposited on it. But how does the loss of copper from the solution get compensated ? the copper anode releases copper ions into the solution, thus compensating for the loss. Since copper sulphate is an ionic compound, it constitutes ions-
$$Cu^{2+}$$ and $$SO_4^{2-}$$
$$CuSO_4 \longrightarrow Cu^{2+} + SO_4^{2-}$$
When electricity is passed through the solution, the cations (i.e. positively charged copper ions) move towards the cathode. Here they gain electrons and get deposited as copper metal.
At cathode:
$$Cu^{2+} + 2e^{-} \rightarrow Cu$$
The sulphate ions remain in the solution. Copper at anode loses electrons and goes into the solution as copper ions to replenish the copper ions deposited at cathode.
An anode:
$$Cu \rightarrow Cu^{2+} + 2e^{-}$$

The deflection occurs because the circuit becomes complete since free ends of the tester are dipped in a solution. The solution is certainly a conducting solution. This is the reason why the compass needle shows a deflection.

(a) Most liquids that conduct electricity are solutions of acids, bases and salts.
(The solutions of acids, bases or salts are conducting in nature. They allow the current to pass through)

Copper ions are positively charged. They are attracted towards the plate which is connected to the negative terminal of the battery. As copper ions are transferred to the thin copper plate, this thin pure copper plate must be connected to the negative terminal of the battery. Consequently, impure copper rod is connected to the positive terminal of the battery. 
Concept insight: When electric current is passed in this arrangement, copper ions from the solution get deposited on pure copper rod (attached to negative terminal) and copper ions from impure copper rod (attached to positive terminal) are liberated into the solution.