Class 8 Science - Chemical Effects of Electric Current CBSE Worksheets Solutions

Q1: Which effect of electric current is utilized for detecting the flow of current through a solution when a compass is used?

Ans: Magnetic effect of electric current is utilized for detecting the flow of current through a solution when a compass is used.

Magnetic effect of Electric Current Q2: What is meant by the chemical effect of electric current? Give an example.

Ans: The passage of an electric current through a conducting liquid causes chemical reactions. The resulting effects are called chemical effects of currents. Example – Deposit of metal formed when electric current is passed through copper sulphate solution (during electroplating).

Chemical Effect of Electric CurrentQ3:  A beaker contains an acidified copper sulphate solution. A copper plate and a carbon rod are kept in this copper sulphate solution. The copper plate is connected to the positive terminal of a battery whereas the carbon rod is connected to the negative terminal of the battery. What happens when electric current is passed through copper sulphate solution?

Ans: When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. From the other electrode, a copper plate, an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from the solution is restored and the process keeps going. This means that copper gets transferred from one electrode to the other.

Q4: Name two metals which are usually electroplated on cheaper metals for making jewelry (or ornaments).

Ans: Silver and gold are usually electroplated on cheaper metals for making jewelry (or ornaments).

Silver and GoldQ5: Why the bulb glows when the electric current passes through it?

Ans: Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing. However, if the current through a circuit is too weak, the filament does not get heated sufficiently and it does not glow.

BulbQ6:  Tap water conducts electricity whereas distilled water does not. Give reason.

Ans: Distilled water is a poor conductor of electricity because it does not contain any dissolved salts in it which can provide it ions to conduct electricity. The distilled water becomes a good conductor of electricity on dissolving a little salt in it. The water that we get from taps is not pure. It may contain several salts dissolved in it. This water is thus a good conductor of electricity.

Q7:  The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?

Ans: A thick rod of impure copper should be connected to the positive terminal of the battery. A thin plate of pure copper should be connected to the negative terminal of the battery. On passing electric current, the metal dissolves from the impure anode and goes into the electrolyte solution. The positively charged ions of metals present in their molten compounds are attracted by the negatively charged electrode.

Q8: Does pure water conduct electricity? If not, what can we do to make it conducting?

Ans: Pure water is free of salts and is a poor conductor. We can add some common salt in pure water to make it conducting.

Q9: In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

Ans: Water is a conductor of electricity, so if the electricity supply is not cut off and firemen come in contact with wet electric switches, electric wires and other electrical appliances, they may get electrocuted.

Q10: What happens when electric current is passed through acidified water?

Ans: When electrodes are immersed in water, and a current is passed through acidified water, then oxygen gas is formed at the positive electrode which is connected to the positive terminal of the battery and hydrogen gas is formed at the negative electrode which is connected to the negative terminal of the battery.

Q11: A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?

Ans: The compass needle deflects more in the case of seawater because due to the presence of a large amount of dissolved salts in it, sea water is a much better conductor of electricity than drinking water.

Q12: What is the advantage of using LED in testing the electrical conductivity of liquids?

Ans: The advantage of using LED in testing the electrical conductivity of liquids is that it glows even when a weak electric current flows through it.

Q13: For electroplating copper on an iron object, which terminal of the battery (positive or negative) is connected to the iron object?

Ans: In the process of electroplating, the metal to be electroplated is taken as cathode (negative) and the one used for coating is chosen as the anode (positive). Thus, negative terminal will be connected to the iron object.

Q14: Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Ans: It is not safe for the electrician to carry out electrical repairs outdoors during heavy downpour because rainwater being a conductor of electricity may cause electrocution of the electrician.

Q15:  Which is the polluting waste generated by electroplating factories?

Ans: The conducting solution used in the electroplating process is the polluting waste generated by electroplating factories.