NCERT Solutions for Class 8th Science
Chapter 14 – CHEMICAL EFFECTS OF ELECTRIC CURRENT
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.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 ____________.
Ans (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_.
Q.2 When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Ans The magnetic needle shows deflection due to the passage or conduction of current through the solution. This shows that the solution is conducting.
Q.3 Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.
Q.4 The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.
Q.5 A tester is used to check the conduction of electricity through two liquids, labeled 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.
Q.6 Does pure water conduct electricity? If not, what can we do to make it conducting?
Ans No. Pure water does not conduct electricity. By adding a pinch of common salt in the pure water it can be made conducting.
Q.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.
Q.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?
Q.9 Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Ans No. This is because rain water contains impurities and hence is a good conductor of electricity. If the electrician carries out electrical repairs outdoors during heavy downpour the rain water on coming in contact with electrical setup may conduct electricity and can cause an electric shock to the electrician.
Q.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?
Q.11 Prepare a list of objects around you that are electroplated.
Q.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 battery and why?