Question 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 cause ______________ 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 _________.
Solution 1.
(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.
Question 2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Solution 2. When the free ends of a tester are dipped into a solution it completes the circuit hence the magnetic needle shows deflection because the solution becomes the conducting solution.
Question 3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.
Solution 3. Following are the three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect:
- Saltwater
- Lemon juice
- Vegetable oil
Question 4. The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.
Solution 4.
The following may be the possible reasons for the bulb not glowing:
- Because of the non-conducting solution the circuit remains incomplete hence, the bulb will not glow.
- weak electric current may flow through the circuit that is unable to make the bulb glow.
Question 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.
Solution 5. (i) liquid A is a better conductor than liquid B.
Liquid A is a better conductor than liquid B because the amount of current flowing through the solution is determined by the conductivity of the solution more the solution is conductive more current will flow through the circuit.
Question 6. Does pure water conduct electricity? If not, what can we do to make it conducting?
Solution 6. Pure water does not contain any type of salt that is why it does not conduct electricity. We can make pure water into a conducting solution by adding a small amount of common salt like NaCl.
Question 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.
Solution 7. Water is a conductor of electricity and it may hurt the fireman that is why the firemen use the water hoses, they shut off the main electrical supply for the area in case of a fire.
Question 8. A child staying in a coastal region tests the drinking water and also seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Solution 8. Seawater contains more amount of salt than drinking water hence it will be the better conductor of electricity. that is why the compass needle deflects more in the case of seawater.
Question 9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpours? Explain.
Solution 9. Rainwater contains a certain amount of salt making it a good conductor of electricity for this reason it is not safe for the electrician to carry out electrical repairs outdoors during a heavy downpour.
Question 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?
Solution 10. Rainwater contains a certain amount of salt making it a good conductor of electricity that is why the compass needle showed deflection when tested it using a tester.
Question 11. Prepare a list of objects around you that are electroplated.
Solution 11. Following are the objects that are electroplated:
- Door handles
- Taps
- Rims of cycle
- Gas burners
- Buckles of belts
- Metallic almirah
Question 12. The process that you saw in Activity 14.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the 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?
Solution 12. The positive terminal of the battery should be connected to a thick rod of the impure copper plate because the copper sulphate solution gets dissociated into copper and sulphate when the electric current is passed through it. The positively charged free electron gets deposited to the negative terminal and the solution will regain the lost amount of copper to the positive terminal of the battery.