NCERT Solutions Class 8th Science Chapter – 14 Chemical Effects of Electric Current Question & Answer

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 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 _______
?‍♀️Answer:
(a) acids, bases, salts
(b) chemical
(c) negative
(d) 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?
?‍♀️Answer: The deflection in magnetic needle shows that the circuit is complete and the solution conducts electricity, i.e., it is a good conductor.

Question 3. Name three liquids, which when tested in the manner shown in Fig. 14.5. may cause the magnetic needle to deflect.

?‍♀️Answer: Vinegar, lemon juice and tap water.

Question 4. The bulb does not glow in the setup shown in Fig. 14.6. List the possible reasons. Explain your answer.

?‍♀️Answer: The bulb may not glow because of the following reasons:
(i) The wires in the circuit may be loosely connected.
(ii) The bulb may be fused.
(iii) The cells may be used up.
(iv) The liquid may be an insulator, i.e., a poor conductor of electricity.

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.
?‍♀️Answer: (i) liquid A is a better conductor than liquid B.

Question 6. Does pure water conduct electricity? If not, what can we do to make it conducting?
?‍♀️Answer: No, pure water doesn’t conduct electricity. But when salt is dissolved in pure water, it conducts electricity.

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.
?‍♀️Answer: The water used in the water hoses is not pure water and is a good conductor of electricity. So, the fire¬men shut off the electric supply before spraying water to save themselves and other people from electrocution.

Question 8. A child staying in a coastal region test 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 ex¬plain the reason?
?‍♀️Answer: The seawater contains a huge amount of salts in comparison to drinking water, hence the seawater is a better conductor of electricity and it produces a stronger magnetic field in the wire and hence deflects the compass needle more.

Question 9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
?‍♀️Answer: No, it is highly dangerous to carry out the electrical repairs outdoors during the heavy downpour. It can cause electrocution, as water is a good conductor of electricity.

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?
?‍♀️Answer: Rainwater is pure water which is an insulator but it gets mixed with air pollutants like sulphur dioxide and nitrogen oxides and form acidic solution, which is a good conductor of electricity. So, the compass needle showed deflection.

Question 11. Prepare a list of objects around you that are electroplated.
?‍♀️Answer: Objects that are electroplated are door handles, taps, rims of cycles, showers, the handlebar of cycles and bikes, gas burner, tin cans, metallic almirahs, buckles of belts, etc.

Question 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?
?‍♀️Answer: The thick rod of impure copper plate is to be attached to the positive terminal of the battery because when electric current is passed through the copper sulphate solution, it gets dissociated into copper and sulphate. The free copper, being positively charged, gets drawn to the negative terminal of the battery and gets deposited on it. On the other hand the loss of copper from the solution is regained from the impure copper rod which is attached to the positive terminal of the battery.

• Thus, lemon juice, vinegar, tap water, milk, curd and water, and soda are good conductors of electricity while vegetable oil, honey, kerosene oil, and distilled water are poor conductors of electricity or insulators.

?‍♀️Answer: The bulb does not glow because distilled water is an insulator, since it does not have dissolved salts.

?‍♀️Answer: The compass needle will show deflection with tap water, lemon juice and sodium chloride solution.

1. Liquid A is a better conductor than liquid B.
2. Liquid B is a better conductor than liquid A.
3. Both liquids are equally conducting.
4. Conducting properties of liquid cannot be compared in this manner.
?‍♀️Answer: Liquid A is a better conductor of electricity because the bulb glows more in it.

Most liquids that conduct electricity are solutions of …………, ………. and …………..
The passage of an electric current through a solution causes ……………….. effects.
If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ……….. terminal of the battery.
The process of depositing a layer of any desired metal on another material by means of electricity is called …………
?‍♀️Answer:
1. acids, bases and salts.
2. change
3. negative
4. electroplating

?‍♀️Answer: It cannot be said for sure that liquid does not conduct electricity because :

• may be the cells are weak.
• may be the current is so weak that it does not heat the filament of the bulb allowing it to glow.

• the connections may be loose.
• the bulb may be defective.
• the cells may be defective.

• Electroplating.
• Refining of impure metals.
• Refining of metal are for obtaining pure metal.

• Decoration of articles by giving them a layer for e.g., silver plating on cutlery.
• Protection of the surface of bases metals which corrode for e.g., iron is plated with chromium.
• Artificial jewellery is plated with silver or gold.

• The articles to be plated should be cleaned throughly to remove dust, grease or any deposit on it.
• Only direct current should be used.
• The temperature around the electroplating equipment should be optimum.

• Take a filter paper soaked in potassium iodide solution to which a pinch of starch is added.
• Place the filter paper on a metal sheet.
• Connect the negative terminal of battery to the metal sheet.
• Write on the paper with the end of the wire connected to the positive terminal.

• The writing appears on the paper. This happens because the when current is passed, the K+ ions are attracted to the metal sheet. The iodide ions (I-) react with starch to turn blue black.

• as indicators in electrical appliances.
• as a point source of light in laser beam torches.
• LEDs emitting white light can be used instead of bulbs.

The longer lead (leg) from the LED should be connected to the positive terminal of the battery and the shorter lead to the negative terminal of the battery.