Lakhmir Singh & Manjit Kaur: Chemical Effects of Electric Current- 3 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Multiple Choice Questions

Q.46. In an activity to check the conduction of electricity through two liquids labelled A and B by using a bulb, it is observed that the bulb glows brightly for liquid A while it glows very dimly for liquid B.
(a) Liquid A is a better conductor than liquid B 
(b) Liquid B is a better conductor than liquid A 
(c) Both liquids are equally conducting 
(d) Conducting properties of liquids cannot be compared in this manner

Correct Answer is Option (a)
Because current flows more easily throughout liquid A than B. Thus, A is a better conductor than liquid B.

Q.47. Which of the following does not conduct electricity?
(a) Vinegar solution
(b) Sugar solution
(c) Lemon juice solution
(d) Caustic soda solution

Correct Answer is Option (b)
Sugar solution does not contain any ions. Thus, it does not conduct electricity.

Q.48. Which of the following metals should be electroplated on a tiffin box made of steel?
(a) Copper
(b) Chromium
(c) Silver
(d) Tin

Correct Answer is Option (d)
Tin should be electroplated on a tiffin box made of steel as it is non-corrosive.

Q.49. Which of the following metals are produced by the electrolysis of their molten compounds?
(A) Copper
(B) Silver
(C) Aluminium
(D) Sodium
(a) A and B
(b) B and C
(c) C and D
(d) Only D

Correct Answer is Option (c)
Both Aluminum and Sodium metals are produced by the electrolysis of their molten compounds because they are not freely available. They need to be extracted from their sources.

Q.50. Which of the following types of energy can be used to decompose water into its elements
(a) Heat energy
(b) Light energy
(c) Chemical energy
(d) Electrical energy

Correct Answer is Option (d)
Electrical energy is used to decompose water into its elements i.e. hydroxide (OH^–) and (H⁺) ions.

Q.51. Which of the following compounds is manufactured by using the chemical effect of electric current?
(a) Ammonium hydroxide
(b) Sodium carbonate
(c) Magnesium hydroxide
(d) Sodium hydroxide

Correct Answer is Option (d)
Sodium hydroxide (NaOH) is manufactured by using the chemical effect of electric current when a sodium salt is electrolysed.

Q.52. Which of the following objects should not be chrome-plated?
(a) Car bumper
(b) Gas stove
(c) Frying pan
(d) Bicycle bell

Correct Answer is Option (c)
Frying pan should not be chrome-plated because it can enter the body by mixing in the food which can prove to be dangerous for the body.

Q.53. Which of the following is a weak electrolyte?
(a) Carbonic acid
(b) Sodium hydroxide
(c) Copper sulphate
(d) Nitric acid

Correct Answer is Option (a)
Carbonic acid is a weak electrolyte because it does not completely dissociate into the aqueous solution.

Q.54. Electrolytes conduct electricity due to the movement of:
(a) Electrodes
(b) Atoms
(c) Electrons
(d) Ions

Correct Answer is Option (d)
Electrolytes conduct electricity due to the movement of ions. Because positive and negative ions conduct electricity.

Q.55. Non-metals are generally non-conductors of electricity. The non-metal whose one of the forms can be used to make electrodes in electrolysis experiments is:
(a) Iodine
(b) Carbon
(c) Silicon
(d) Phosphorus

Correct Answer is Option (b)
The non-metal whose one of the forms can be used to make electrodes in electrolysis experiments is Carbon and the form is graphite form. We come across graphite electrodes because it is a good conductor.

Q.56. The decomposition produced by passing current through a conducting liquid is called
(a) Dialysis
(b) Hydrolysis
(c) Electrolysis
(d) Electroplating

Correct Answer is Option (c)
Electrolysis is the decomposition produced by passing current through a conducting liquid. The solution is dissociated into ions.

Q.57. Which of the following is not an application of the chemical effect of electric current
(a) Electroplating of metals
(b) Purification of metals
(c) Decomposition of elements
(d) Decomposition of compounds

Correct Answer is Option (c)
Decomposition of elements is not an application of the chemical effect of electric current. Electroplating, purification and decomposition of compounds can be done with the help of chemical effect of electric current.

Q.58. One of the following is not used for electroplating metal articles. This one is:
(a) Nickel
(b) Chromium
(c) Sodium
(d) Silver

Correct Answer is Option (c)

Sodium is not used for electroplating metal articles. Because it is a corrosive metal.

Q.59. An arrangement having two carbon rods kept in a conducting liquid in a vessel is known as
(a) Rechargeable cell
(b) Storage cell
(c) Biological cell
(d) Electrolytic cell

Correct Answer is Option (d)
An electrolytic cell is an arrangement having two carbon rods kept in a conducting liquid in a vessel. This is the process setup for the electrolysis of electrolytes.

Q.60. Which of the following effects is not produced by the chemical reactions brought about by an electric current?
(a) Bubbles of gases on electrodes
(b) Deposits of metals on electrodes
(c) Change in color of solution
(d) Formation of a precipitate

Correct Answer is Option (d)
Formation of a precipitate is not produced by the chemical reactions brought about by an electric current. Because it does not involves any chemical reaction but involves chemical changes in the solutions

Q.61. Which of the following can be electroplated with chromium?
(A) Bakelite
(B) Graphite
(C) Steel
(D) Teflon
(a) A and B
(b) B and C
(c) only C
(d) B and D

Correct Answer is Option (b)
Graphite and Steel can be electroplated with chromium. Chrome plating is not done on graphite and steel electrodes.

Q.62. In order to obtain a coating of silver metal on a flower vase made of copper, the electrolyte has to be:
(a) Silver nitrate solution
(b) Copper nitrate solution
(c) Sodium nitrate solution
(d) Copper sulphate solution

Correct Answer is Option (a)
In order to obtain a coating of silver metal on a flower vase made of copper, the electrolyte has to be silver nitrate solution. Because the silver ions will come from the electrolyte.

Q.63. The process of purification of an impure metal is like:
(a) Electroplating a metal on the same type of metal
(b) Electroplating a metal on another type of metal
(c) Producing a chemical compound by electrolysis
(d) Decomposing a chemical compound by electrolysis.

Correct Answer is Option (a)
The process of purification of an impure metal is like electroplating a metal on the same type of metal. The pure metal is removed and deposited on the pure metal.

Q.64. The device which can be used to detect very small current flowing in an electric circuit is:
(a) LEAD
(b) dB
(c) MCB
(d) LED

Correct Answer is Option (d)
LED Light emitting diode is used to detect very small current flowing in an electric circuit.

Q.65. If plus sign (+) denotes the positive electrode and minus sign (-) denotes the negative electrode, then which of the following statement is correct for an iron spoon to be copper-plated?
(a) Iron spoon (+),copper plate(-), Iron sulphate electrolyte
(b) Iron spoon(-), copper plate(+), Iron sulphate electrolyte
(c) Copper plate(-), Iron spoon(+), Copper sulphate electrolyte
(d) Copper plate(+), Iron spoon(-), Copper sulphate electrolyte

Correct Answer is Option (d)
Copper plate(+), Iron spoon(-), Copper sulphate electrolyte is the correct setup combination for electroplating. Because the anode is made the metal to be deposited and cathode to the one on which it is electroplated.

Q.66. A student staying in a coastal region tests the drinking water and also the sea water ‘With a circuit in which a part of the connecting wire is wound around a matchbox containing compass. He finds that the compass needle deflects more in the case of sea water. Can you explain the reason?

Sea water is a better conductor because it contains sodium and chloride ions in large amounts. These ions make the solution conducting and thus, sea water is considered better conductor than the drinking water which does not contain ions. The ions of drinking water are removed while removed while purifying it.

Q.67. When an electric current is passed through a cut potato for a considerable time, a coloured spot is formed around one of the electrodes:
(a) What is the colour of the spot?
(b) Around which electrode (positive or negative electrode) the coloured spot is formed?
(c) Which effect of electric current is involved in this case?

(a) The spot color is Greenish blue.
(b) The coloured spot is formed around the positive electrode.
(c) This is known as Chemical effect.

Q.68. In the process of purification of copper metal, a thin plate of pure copper and a thick rod of impure copper are used as electrodes, and a metal salt solution is used as an electrolyte:
(a) Which electrode is connected to the positive terminal of the battery?
(b) Which electrode is connected to the negative terminal of the battery?
(c) Which metal salt solution is taken as electrolyte?

(a) Thick rod of impure copper is connected to the positive terminal of the battery.
(b) Thin plate of pure copper is connected to the negative terminal of the battery.
(c) Copper sulphate solution is taken as electrolyte.

Q.69. A student had heard that rainwater is as good as distilled water. So, he collected some rainwater in a clean glass beaker and tested it. To his surprise he found that the compass needle showed deflection. What could be the reason? 

Rain water can collect salts from the atmosphere has some dissolved salts whereas the distilled water does not. Thus, the rainwater showed the deflection because it conducts electricity.

Q.70. Name three liquids which when tested in the manner shown in figure given along side may cause the magnetic needle of compass to deflect.

The Liquids that conduct electricity will cause the magnetic needle to deflect because the electric current is capable of producing magnetic effect. The liquids like lemon juice, salt water and vegetable oil allow electricity to pass through them. Hence, these liquids can be used as in the beaker to show the given effect.