Chemical Effects of Electric Current - Class 8 : NCERT Exercise Questions



 

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 ______________.
Sol. (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?
Sol. The deflection in the magnetic needle is observed, when the electric current flows through the wounded wire. Hence, it means the solution is a good conductor of electricity. This is the reason magnetic needle shows deflection when the free ends of a tester are dipped into a solution.

Q.3 Name three liquids, which when tested in the manner shown in Fig., may cause the magnetic needle to deflect.
Sol. The names of three liquids which may cause the magnetic needle to deflect are lemon juice, salt water and vinegar.

Q.4 The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.
Sol. The lists of possible reasons for the bulb not glowing are:
(i) The circuit might be incomplete.
(ii) The bulb might be fused.
(iii) Liquid in the beaker might be non-conducting.
(iv) Insufficient charge of battery which might be responsible for bulb not glowing.

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

Q.6 Does pure water conduct electricity? If not, what can we do to make it conducting?
Sol. Pure water does not conduct electricity because there are no salts dissolved in it. Therefore, it is a poor conductor of electricity. To make it conducting, we can add impurities like common salt, lemon juice, vinegar, etc.

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.
Sol. Water usually contains impurities which makes it a good conductor of electricity. If the electrical supply is not shut off, then electricity may pass through water and harm the firemen. This is the reason in case of a fire, before the firemen use the water hoses; they shut off the main electrical supply for the area.

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?
Sol. The amount of salts dissolved in the sea water is more than the drinking water. The drinking water is normally treated and purified which removes impurities present in it. Therefore, the compass needle deflects more in the case of sea water.

Q.9 Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Sol. No, it is not safe for the electrician to carry out electrical repairs outdoors during heavy downpour because the rain water contains dissolved salts. This makes rain water a good conductor of electricity; hence, it might cause electrical shock to 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?
Sol. The various air pollutants emitted from industries get dissolved in the rain water. This makes it impure while distilled water has no such salts dissolved in it. Hence, rain water allows electricity to pass through it, and so compass needle showed deflection, while distilled does not allow electricity to pass through it.

Q.11 Prepare a list of objects around you that are electroplated.
Sol. The following is a list of objects around me which are electroplated:
(i) Cars, buses, etc. are electroplated with chromium to give them shiny appearance.
(ii) Artificial jewellery items are either silver or gold plated.
(iii) Door handles, metal items, etc. are zinc plated.
(iv) Cans are tin plated.
(v) Iron used in building constructions is coated with zinc to prevent corrosion and rusting of iron.

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?
Sol. The impure copper plate should be connected to the positive terminal, while the pure copper plate should be connected to the negative terminal. This is because the copper ions are positively charged and will be attracted towards the negative terminal of the battery.



3 Comments

Leave a Reply

FREE CBSE Video Solutions & Chapter Video Lectures Watch
NOW