Free Chemical Effects of Electric Current 02 Practice Test - 8th Grade 

Question 1

Rohit has an impure copper plate and wants to purify it by electroplating. Using an electrolytic setup, he can do this by 

 

A.

using the impure copper plate as the positive terminal electrode.

B.

using impure copper plate as the negative terminal electrode.

C.

breaking the impure copper plate into 2 halves and using them as electrodes.

D.

simply placing the impure copper plate in the electrolyte.

SOLUTION

Solution : A

Rohit can purify the copper plate and get the pure copper by using the below mentioned electrolytic setup. On using the impure copper plate as the positive terminal electrode, the metal dissolves from impure copper plate and goes in the copper sulphate solution. The dissolved metal present in the solution is deposited on the cathode and the impurities are left in the copper sulphate solution. 

Question 2

A child staying in a coastal region uses his tester (consisting of a magnetic needle) with drinking water and sea water. He observes that

A.

magnetic needle deflects more in the case of sea water.

B.

magnetic needle deflects more in the case of drinking water

C.

magnetic needle does not deflect in any case.

D.

magnetic deflection will be same in both cases

SOLUTION

Solution : A

Sea water is more conducting compared to drinking water, as the former has more salts. So, more current flows through sea water than through drinking water. Hence, when tested with a tester, the magnetic deflection will be more in the case of sea water.

Question 3

In which of the following examples chemical effects of electric current is desirable?

A.

Production of spark at the electrodes.

B.

Deposition of metal on the electrodes.

C.

Production of heat.

D.

Production of Light.

SOLUTION

Solution : B

When an electric current is passed through a solution, positive ions move towards the electrode which is connected to the negative terminal of the battery. The positive ions take electrons from the negative terminal and may get deposited at the electrode. 

Question 4

Which of the following is a bad conductor of electricity?

A. ORS drink
B. Distilled water
C. Tap water
D. Salt water

SOLUTION

Solution : B

Distilled water does not have any ions for the conduction of electricity, while salt water, tap water, and ORS drink have salts present in them which form ions in water and conduct electricity. Hence, distilled water is a bad conductor of electricity.

Question 5

Electrodes are immersed in water and electric current is passed through it. Which of the following statements is correct?

A.

Oxygen bubbles will be formed at the electrode which is connected to the negative terminal of the battery

B.

Hydrogen gas will be formed at the electrode which is connected to the positive terminal of the battery

C.

No gas is formed at any electrode

D.

Hydrogen gas will be formed at the electrode which is connected to the negative terminal of the battery

SOLUTION

Solution : D

H+ ions move towards the electrode which is connected to the negative terminal of the battery, gain electrons and get released as H2 gas. 2H++2e−→H2

Question 6

The process of depositing a layer of a desired metal on another material by means of electricity is called __.

SOLUTION

Solution :

The process is known as electroplating. In this process, electrical energy is converted into chemical energy.

Question 7

A cell is an example of conversion of:

A. Magnetic energy into chemical energy
B. Electrical energy into chemical energy
C. Chemical energy into electrical energy
D. Chemical energy into magnetic energy

SOLUTION

Solution : C

When a cell is connected in a closed circuit, chemical reactions occur inside the cell which results in the release of charge and this charge flows through the circuit as an electric current. Hence, a cell converts chemical energy into electrical energy.

Question 8

The decomposition of an electrolyte when electricity is passed through it is called:

A. Conduction
B. Electroplating
C. Electrolysis
D. Electrorefining

SOLUTION

Solution : C

Electrolysis is the decomposition of an electrolyte when electricity is passed through it. It is a chemical change and results in the formation of new substances.

Question 9

Due to chemical effect of electric current, substances can be split or combined  at the molecular level.
 

A. True
B. False

SOLUTION

Solution : A

Electric current, when passed through a salt solution through a specific apparatus, can create a chemical change. Such a process is called Electrolysis. Obtaining a chemical change with the use of electrical energy is known as Chemical Effect of Electricity.

Question 10

Identify the examples of the bad conductors of electricity from the following options.

A. Sulphuric acid
B. Air
C. Rubber 
D. H2O

SOLUTION

Solution : B, C, and D

To be a good electric conductor, a material needs to have free electrons or ions.
Sulphuric acid has H+ and SO−4 ions.
H2O is pure water which does not have any salts and is a bad conductor of electricity.
Air and rubber are also bad conductors as they have no free electrons or ions.
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