NCERT Class 8 Science Chapter 14 - Chemical Effects of Electric Current Extra Questions

Chapter 14 - Chemical Effects of Electric Current Extra Questions

Fill in the blanks
1. Substances that conduct electricity are called
conductors.

2. Substances that do not conduct electricity are called
insulators.

3. A cation has
positive charge.

4. Some liquids are
good conductors of electricity and some are bad conductors of electricity.

5. Distilled water is an
insulator.

6. Distilled water when mixed with salts becomes a
good conductor of electricity.

7. Light Emitting Diodes (LED) glow even when a
weak electric current flows through it.

8. The passage of an electric current through a conducting solution causes
chemical reaction.

9. Change in colour is an example of the
chemical effect of current.

10. There are
2 wires attached to an LED.

11. In an LED, the longer lead is attached to the
positive terminal of the battery and the shorter lead to the negative terminal.

12. Chromium has a
shiny appearance.

13. Distilled water is made by removing all
impurities.

14. Iron tends to
corrode and rust.

15. A coating of
zinc is deposited on iron to protect it from corrosion and formation of rust.

16. An electric lamp glows due to
heating effect of electric current.

17. Electrodes are
conductors.

18. The deflection in
magnetic compass shows that current is passing.

19.
Chromium does not corrode easily.

20. An electrolyte is a
liquid.

Answer the following:
21. What do you understand by good conductors of electricity?
Answer:
The substances which allow electricity to pass through them are called good conductors.

22. What do you understand by bad conductors of electricity?
Answer:
The substances which don’t allow electricity to pass through them are called bad conductors.

23. Name any three liquids that may cause the magnetic needle to deflect.
Answer:
Vinegar, lemon juice hydrochloric acid etc.

24. Name the three effects of electric current.
Answer:
There are 3 types of effects of electric current. They are
• Heating
• Magnetic
• Chemical

25. 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 as
• The wires in the circuit may be loosely connected.
• The bulb may be fused.
• The liquid may be a poor conductor of electricity.
• The cells may be used up.

26. 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.

27. List some objects that are electroplated.
Answer:
Some objects that are electroplated include handles of bike and car, jewellery, tin cans etc.

28. Define electroplating.
Answer:
The process of depositing a layer of any desired material on another material by means of electricity is called electroplating.

29. Write a short note on LED.
Answer:
The full form of LED is Light Emitting Diode. In an LED, the longer lead is attached to the positive terminal of the battery and the shorter lead to the negative terminal.

30. Why is a layer of zinc coated over iron?
Answer:
A layer of zinc is coated over iron to prevent it from corrosion and rust.

Multiple Choice Questions
31. Which of the following is a bad conductor of electricity?
a) Distilled water
b) Silver nitrate
c) Sulphuric acid
d) Copper sulphate
Answer:
a) Distilled water

32. Which of the following does not conduct electricity?
a) Sugar solution
b) Vinegar solution
c) Lemon juice solution
d) Caustic soda solution
Answer:
a) Sugar solution

33. An electric current can produce
a) heating effect
b) chemical effect
c) magnetic effect
d) all of these
Answer:
d) all of these

34. Pure or distilled water is a
a) poor conductor
b) good conductor
c) both a) and b)
d) none of these
Answer:
a) poor conductor

35. Which of the following is a good conductor?
a) Brick
b) Steel
c) Plastic
d) Cotton
Answer:
b) Steel

36. Polythene is
a) a conductor
b) an insulator
c) both a) and b)
d) none of these
Answer:
b) an insulator

37. Electroplating is based on
a) heating effect of electricity
b) chemical effect of electricity
c) physical effect of electricity
d) magnetic effect of electricity
Answer:
b) chemical effect of electricity

38. Copper is
a) a good conductor
b) an insulator
c) both a) and b)
d) none of these
Answer:
a) a good conductor

39. Waste from an electroplating factory must be disposed off
a) in the nearby river
b) in the nearby pond
c) in the nearby cornfield
d) according to the disposal guidelines of waste management bodies
Answer:
d) according to the disposal guidelines of waste management bodies

40. An electrolyte is
a) a metal
b) a liquid that conducts current
c) a non-metal
d) none of these
Answer:
b) a liquid that conducts current

41. Flow of electron is called
a) electrolyte
b) electroplating
c) electrodes
d) electric current
Answer:
d) electric current

42. Which is not a non-electrolyte?
a) Ethyl alcohol
b) Sodium chloride
c) Urea
d) Sodium solution
Answer:
b) Sodium chloride

43. An electric lamp glows due to
a) heating effect
b) magnetic effect
c) chemical effect
d) physical effect
Answer:
a) heating effect

44. Electroplating prevents
a) corrosion
b) passing of current
c) dissociation
d) shining
Answer:
a) corrosion

45. Which of the following is not used for electroplating metal articles?
a) Nickel
b) Silver
c) Chromium
d) Sodium
Answer:
d) Sodium

46. Iron objects can be protected by electroplating them with
a) chromium
b) nickel
c) zinc
d) all of these
Answer:
d) all of these

Match the following

Answer:


True or False
State whether the given statements are true or false.
47. Rubber is a good conductor of electricity. (
False)

48. Plastics are poor conductor of electricity. (
True)

49. All liquids conduct electricity. (
False)

50. Distilled water is free of salt. (
True)

51. Pure water conducts electricity. (
False)

52. Most liquids that conducts electricity are solutions of acids, bases and salts. (
True)

53. Electroplating is based on magnetic effect of electricity. (
False)

54. Small amount of some mineral salts are naturally present in water. (
True)

55. Chromium is carcinogenic. (
True)

56. An electric bulb glows due to chemical effect of electricity. (
False)

57. Distilled water when mixed with salt conducts electricity. (
True)

58. LED is an electric bulb which is used in a tester. (
True)

59. Deflection in compass needle is due to magnetic effect of current. (
True)

60. When electric current is passed through the copper sulphate solution, copper and sulphate ions are dissociated. (
True)

61. In an LED bulb, the shorter lead is connected to the positive terminal of the battery. (
False)

62. Electric current produces a magnetic effect. (
True)

63. Some liquids are good conductors of electricity and some are poor conductors of electricity. (
True)

64. Chromium has a shiny appearance. (
True)

65. Jewellery makers electroplate silver and gold on expensive metals. (
False)

66. Electroplating wastes are useful to human health and environment. (
False)

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