NCERT Solutions for Class 8 Science Chapter 14 Chemical Effects of Electric Current provides ready solutions for all the questions given in the NCERT Class 8 Science textbook. Electric Current’s chemical effect is the basic topic that is required to be understood to avoid difficulty in all your future endeavors. This solution comprehensively makes you understand the topic and clear your doubts by its answers.
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NCERT Solutions for Class 8 Science Chapter 14: Chemical effects of electric current
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
(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 u 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?
The deflection of the magnetic needle shows that the circuit is complete and the solution conducts electricity.
3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.
The liquids which will cause the deflection of the magnetic needle are vinegar, lemon juice and tap water.
4. The bulb does not glow in the setup shown in Fig.14.10. List the possible
reasons. Explain your answer.
The bulb may not glow because of the following reasons:
(i) The wires in the circuit may not be properly connected.
(ii) The bulb may be fused.
(iii) The cells may be used up.
(iv) The liquid may be a poor conductor of electricity.
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.
Option (i) is the correct answer because the conductivity of the solution determines the strength of current flowing through the solution. Greater the conductivity, greater will be the quantity current passing through the solution and vice versa.
6. Does pure water conduct electricity? If not, what can we do to make it
Pure water does not conduct electricity because it does not contain any salt. Pure water can be made conducting by adding a small amount of common salt (Sodium Chloride ie,.NaCl).
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.
The water used in the water hoses is not pure water and thus it is a good conductor of electricity. So, the firemen shut off the electric supply before spraying water to save themselves and other people from electrocution.
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?
A huge amount of salt is dissolved in the seawater. Hence the seawater is a better conductor of electricity. This is the reason why salt water produces a stronger magnetic field in the wire thereby deflecting the compass needle more.
9. Is it safe for the electrician to carry out electrical repairs outdoors during
heavy downpour? Explain.
No, it is not safe to carry out the electrical repairs outdoors during the heavy downpour. Water being a good conductor of electricity can cause electrocution if repair work is carried by the electrician in heavy downpour.
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?
Rainwater contains a certain amount of dissolved salts. This makes it conductive and thus giving rise to deflection in the compass needle.
11. Prepare a list of objects around you that are electroplated.
The list of objects around us which are electroplated are:
The exterior parts of automobiles are electroplated with chromium in order to give them shiny
Silver ornaments are coated with a thin layer of gold.
Iron used for construction purposes are coated with a zinc in order to protect them from corrosion and rusting.
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?
The thick rod of impure copper plate should be connected to the positive terminal of the battery because when electric current passes through the copper sulphate solution, it dissociates into copper and sulphate ions. The free copper, being positively charged, gets attracted to the negative terminal of the battery and gets deposited on it. On the other hand the copper ions from the impure copper rod attached to the positive terminal of the battery maintain the supply of copper ions in the solution.