Chapter 10. CHEMICAL EFFECTS OF ELECTRIC CURRENT

Exercises

1. 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______________ .

Answer : (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.

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

Answer : Yes, I can explain the reason for the deflection of the magnetic needle when the free ends of a tester are dipped into a solution. The deflection is due to the presence of an electric current in the solution. The solution may contain ions that can conduct electricity. When the tester is connected to a voltage source, the flow of electric current through the solution causes a magnetic field, which deflects the magnetic needle.

3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Answer : Salt weter , lemon juice and vinegar  .

4. The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

Answer : The list of the possible reasons are :

(i) When the liquid does not allow the electric current to pass, the circuit of the tester is incomplete, and the bulb does not glow.

(ii) In some situations even though the liquid is conducting, the bulb may not glow.

(iii) If the current through a circuit is too weak, the filament does not get heated sufficiently and then the bulb does not glow.

5. 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.

Answer :  The correct conclusion would be (i) liquid A is a better conductor than liquid B.

[ This is indicated by the fact that the bulb of the tester glows brightly for liquid A, suggesting that it allows a larger flow of electric current compared to liquid B, where the bulb glows very dimly.]

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

Answer : No, pure water does not conduct electricity as it does not contain ions. To make it conducting, we can add a small amount of an electrolyte, such as salt, to create ions in the water.

7. 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.

Answer : Firemen shut off the main electrical supply before using water hoses because water and electricity can be very dangerous together. Turning off the power helps prevent electrical shocks and further damage during the firefighting process.

8. 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?

Answer : The compass needle deflects more in the case of seawater because seawater contains dissolved salts and minerals, which make it a better conductor of electricity compared to drinking water. The higher conductivity leads to a stronger magnetic field and greater deflection of the compass needle.

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

Answer : No, it is not safe for an electrician to carry out electrical repairs outdoors during a heavy downpour. Water is a good conductor of electricity, and the presence of rain increases the risk of electrical shock or short circuits. Working with electricity in wet conditions can be extremely dangerous and should be avoided.

10. Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater 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?

Answer : The deflection of the compass needle in Paheli's rainwater sample could be due to the presence of dissolved minerals or impurities in the water, which make it slightly conductive and cause the deflection.

11. Prepare a list of objects around you that are electroplated.

Answer : The list of some common objects around us that might be electroplated :

(i) Chromium Plating: Chromium plating is a process of coating an object with a thin layer of chromium metal. It is commonly used to enhance the appearance of objects and provide them with a shiny, reflective surface.

Gold Plating: Gold plating involves depositing a thin layer of gold onto the surface of an object. Gold plating is often used in jewelry-making to create gold-plated jewelry pieces that are more affordable than solid gold.

Zinc Plating: Zinc plating is a process in which a layer of zinc is applied to the surface of an object . It is primarily used as a protective coating to prevent corrosion.

12. 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 transfered to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Answer : In the process of purification of copper, the thin plate of pure copper should be attached to the positive terminal of the battery. This is because, during electrolysis, positive ions are attracted towards the negative electrode (cathode) where reduction takes place. In this case, the positive copper ions ( ) present in the impure copper rod will be attracted towards the negative electrode (cathode), which is the thin plate of pure copper. As a result, the copper ions will be reduced and deposited onto the pure copper plate, leading to the transfer of pure copper from the impure rod to the thin copper plate.