NCERT Solutions of Chapter: Chemical Effects of Electric Current. NCERT Solutions along with worksheets and notes for Class 8.
(1) Fill I 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.
(2) When the free ends of a tester are dipped into a solution, the magnetic needle shows deflation. Can you explain the reason?
Ans- When the free ends of a tester are dipped into a solution, the magnetic needle shows deflation. It happens because solution is a good conductor of the electricity which passes electricity and compass deflated.
(3) Name three liquids, which when tested in the manner shown in fig below, may cause the magnetic needle to deflate.
Ans-Tap water, lemon juice solution and caustic soda solution in distilled water are three liquids which when tested in the manner shown in fig below, may cause the magnetic needle to deflate.
(4)The bulb does not glow in the setup shown in fig below. List the possible reasons. Explain your answer.
Ans- Reasons of not glowing of bulb are
(i) Bulb may be fused.
(ii) Solution is poor conductor of electricity.
(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 better conductor than liquid A.
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this mannered.
Ans- Liquid A is better conductor than liquid B.
(6)Does pure water conduct electricity? If not, what can we do to make it conducting?
Ans- No, pure water can not conduct electricity. We have to add acid, bases or salt in it. Therefore, we will get acid solution, base solution or salt solution respectively. These solutions are good conductor of electricity.
(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.
Ans- Tap water is a good conductor of electricity. If firemen will not shutoff the main electrical supply for the area, firemen will get electric shock.
(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?
Ans- Seawater is a solution of salt and many other impurities. Therefore, it is very good conductor of the electricity. So, it allows electric current to flow. While drinking water is also good conductor of the electricity but it is not salt solution. Therefore, it allows less electric current to flow.
(9) Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
No, water is a good conductor of electricity. Therefore, at the time of heavy rain outdoors repair can give electric shock to electrician.
(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 reason?
Ans- Rain water has some impurities. Therefore, it allows electricity to pass and needle deflates.
(11) Prepare a list of objects around you that are electroplated.
Ans- List of things that are electroplated-
(i) Aluminum rods of furniture.
(ii) Imitated ornaments
(iii) Show pieces
(iv) Handles of doors
(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 transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Impure copper electrode should be attached to the negative terminal because dissociates copper gets drawn to the negative terminal and deposited on it.
Pure copper electrode should be attached to the positive terminal because dissociates copper gets drawn from the positive terminal and deposited on copper plate at negative terminal.