Lesson: Chemical Effects of Electric Current

Fill in the blanks.

(a)   Most liquids that conduct electricity are solutions of ________, _______ and ________.

(b)   The passage of an electric current through a solution causes _________ effects.

(c)   If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the __________ terminal of the battery.

(d)   The process of depositing a layer of any desired metal on another material by means of electricity is called _________.

(a)   Most liquids that conduct electricity are solutions of acids, bases and salts.

(b)   The passage of an electric current through a solution causes chemical effects.

(c)   If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.

(d)   The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Conduction of electricity takes place through the solution and produces magnetic effect.  So, when the free ends of a tester are dipped into a solution, the needle shows deflection.

Name three liquids, which when tested in the manner shown in the figure below, may cause the magnetic needle to deflect.

Liquids like lemon juice, salt water and vegetable oil cause the magnetic needle to deflect.

The bulb does not glow in the setup shown in the figure given below. List the possible reasons. Explain your answer.

Following are the several possible reasons for not glowing of the bulb:

(a)   The bulb may be fused.

(b)   Connection may be loose or faulty.

(c)   If the bulb does not glow even after checking and replacing the connections, that means the solution does not conduct electricity. A solution, which is a poor conductor of electricity, does not allow much current to pass through it.

A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that
(i) liquid A is a better conductor than liquid B.
(ii) liquid B is a better conductor than liquid A.
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.

(i) Liquid A is a better conductor than liquid B.

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

No. Pure water does not conduct electricity. By dissolving a pinch of common salt, pure water can be made a conductor of electricity.

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.

Water is a conductor of electricity. So, in case of fire, if the electric supply for the area is not shut off then electricity may pass through water and electrocute the firemen. Therefore, the main electric supplies are shut down for the area, before using water hoses.

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?

Sea water contains more dissolved salts than the drinking water. Hence, it is a better conductor than drinking water. That is why; the compass needle deflects more in sea water than in the drinking water.

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

No, it is very risky and unsafe for the electrician to carry out electrical repairs outdoors during downpour because rain water carries impurities dissolved in it, while it comes down.  Due to the presence of these impurities, rain water can conduct electricity, owing to which the electrician may be electrocuted while working outdoors during heavy downpour.

Paheli had heard that rain water is as good as distilled water. So, she collected some rain water in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reasons?

Rain water has many impurities dissolved in it while coming down. Due to the presence of these impurities, rain water becomes a conductor of electricity, whereas, distilled water does not contain any impurities in it.  Hence, while rain water allows electricity to pass through it, distilled water does not.

Prepare a list of objects around you that are electroplated.

·         Car bumpers, cycle rims, and cycle handles are chromium plated.

·         Artificial jewelleries are gold or silver plated.

·         Iron used, in constructing buildings, is coated with a layer of zinc.

The process that you saw in an activity 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 the battery and why?

Electrode of impure copper is connected to the positive terminal of the battery. This is because copper ion is positively charged and it is attracted towards the plate which is connected to the negative terminal of the battery. As copper ions are transferred to the thin pure copper plate, the copper plate must be connected to the negative terminal of the battery. Consequently, impure copper rod should be connected to the positive terminal of the battery.