CBSE Class 12 Chemistry Electrochemistry VBQs

Question. During the electrolysis of an electrolyte, the number of ions produced, is directly proportional to the:
a. Time consumed
b. Electro chemical equivalent of electrolysis
c. Quantity of electricity passed
d. Mass of electrons
Answer : C

Question. Which of the following is non-electrolytes?
a. NaCl
b. CaCl₂
c. C₁₂H₂₂O₁₁
d. CH₃COOH
Answer : C

Question. When a molten ionic hydride is electrolysed?
a. Hydrogen is liberated at the cathode
b. Hydrogen is liberated at the anode
c. There is no reaction
d. H− ions produced migrate to the cathode
Answer : B

Question. The passage of current liberates H₂ at cathode and Cl₂ at anode. The solution is:
a. Copper chloride in water
b. NaCl in water
c. H₂SO₄
d. Water
Answer : B

Question. In electrolysis of aqueous copper sulphate, the gas at anode and cathode is:
a. O₂ and H₂
b. SO₂ and H₂
c. H₂ and O₂
d. SO₃ and O₂
Answer : A

Question. On passing 3 ampere of electricity for 50 minutes, 1.8 gram metal deposits. The equivalent mass of metal is:
a. 20.5
b. 25.8
c. 19.3
d. 30.7
Answer : C

Question. Use of electrolysis is:
a. Electroplating
b. Electro-refining
c. a. and b. both
d. None of these
Answer : C

Question. During the electrolysis of fused NaCl, which reaction occurs at anode?
a. Chloride ions are oxidized
b. Chloride ions are reduced
c. Sodium ions are oxidised
d. Sodium ions are reduced
Answer : A

Question. Which of the following liberate hydrogen on reaction with dilute H₂SO₄ ?
a. Fe
b. Cu
c. Al
d. Hg
Answer : C

Question. . Electrolysis of molten anhydrous calcium chloride produces:
a. Calcium
b. Phosphorus
c. Sulphur
d. Sodium
Answer : A

Question. When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrodes are?
Cathode                          Anode
a. Pure zinc                  Pure copper
b. Impure sample         Pure copper
c. Impure zinc              Impure sample
d. Pure copper             Impure sample
Answer : S

Question. In the electrolytic cell, flow of electrons is from:
a. Cathode to anode in solution
b. Cathode to anode through external supply
c. Cathode to anode through internal supply
d. Anode to cathode through internal supply
Answer : D

Question. An electric current is passed through an aqueous solution of the following. Which one shall decompose?
a. Urea
b. Glucose
c. AgNO₃
d. Ethyl alcohol
Answer : C

Question. How many atoms of calcium will be deposited from a solution of CaCl₂ by a current of 25 mill amperes flowing for 60 seconds?
a. 4.68×10¹⁸
b. 4.68×10¹⁵
c. 4.68×10¹²
d. 4.68×10⁹
Answer : A

Question. An electrolytic cell contains a solution of Ag₂SO₄ and have platinum electrodes. A current is passed until 1.6 gm of O₂ has been liberated at anode. The amount of silver deposited at cathode would be :
a. 107.88 gm
b. 1.6 gm
c. 0.8 gm
d. 21.60 gm
Answer : D

Question. The atomic weight of Al is 27. When a current of 5 Faradays is passed through a solution of Al⁺⁺⁺ ions, the weight of Al deposited is:
a. 27 gm
b. 36 gm
c. 45 gm
d. 39 gm
Answer : C

Question. Conductivity (unit Siemen’s) is directly proportional to area of the vessel and the concentration of the solution in it and is inversely proportional to the length of the vessel then the unit of the constant of proportionality is:
a. Sm mol⁻¹
b. Sm² mol⁻¹
c. S⁻² m² mol⁻²
d. S² m² mol⁻²
Answer : B

Question. On passing 0.5 faraday of electricity through NaCl, the amount of Cl deposited on cathode is:
a. 35.5 gm
b. 17.75 gm
c. 71 gm
d. 142 gm
Answer : B

Question. What is the amount of chlorine evolved when 2 amperes of current is passed for 30 minutes in an aqueous solution of NaCl:
a. 66 g
b. 1.32 g
c. 33 g
d. 99 g
Answer : B

vThree faradays of electricity are passed through molten Al₂O₃ , aqueous solution of CuSO₄ and molten NaCl taken in different electrolytic cells. The amount of Al,Cu and Na deposited at the cathodes will be in the ratio of:
a. 1 mole : 2 mole : 3 mole
b. 3 mole : 2 mole : 1mole
c. 1 mole : 1.5 mole : 3 mole
d. 1.5 mole : 2 mole : 3 mole
Answer : C

Question. 5 amperes is passed through a solution of zinc sulphate for 40 minutes. Find the amount of zinc deposited at the cathode:
a. 40.65 gm
b. 4.065 gm
c. 0.4065 gm
d. 65.04 gm
Answer : B

Question. In an electroplating experiment mg of silver is deposited, when 4 amperes of current flows for 2 minutes. The amount (in mgs) of silver deposited by 6 amperes of current flowing for 40 seconds will be?
a. 4m
b. m/2
c. m/4
d. 2m
Answer : B

Question. The molar conductivity is maximum for the solution of concentration:
a. 0.001 M
b. 0.005 M
c. 0.002 M
d. 0.004 M
Answer : A

Question. In infinite dilutions, the equivalent conductance’s of Ba²⁺ and Cl^– are 127 and 76 ohm⁻¹ cm⁻¹ eqvt⁻¹. The equivalent conductivity of BaCl₂ at indefinite dilution is:
a. 101.5
b. 139.5
c. 203.5
d. 279.5
Answer : B

Question. If X is the specific resistance of the solution and M is the molarity of the solution, the molar conductivity of the solution is given by:
a. 1000X/M
b. 1000/MX
c. 1000M/X
d. MX/1000
Answer : B

Question. Which of the following conducts electricity?
a. Fused NaCl
b. CO₂
c. Br₂
d. Si
Answer : A

Question. When electric current is passed through a cell having an electrolyte, the positive ions move towards the cathode and the negative ions towards the anode. If the cathode is pulled out of the solution?
a. The positive and negative ions will move towards the anode
b. The positive ions will start moving towards the anode, the negative ions will stop moving
c. The negative ions will continue to move towards the anode and the positive ions will stop moving
d. The positive and negative ions will start moving randomly
Answer : D

Question. The unit of molar conductivity is:
a. Ω⁻¹cm⁻² mol⁻¹
b. Ω cm⁻² mol⁻¹
c. Ω⁻¹cm² mol⁻¹
d. Ω cm² mol
Answer : C

Question. Amount of electricity that can deposit 108 gm of silver from AgNO₃ solution is:
a. 1 ampere
b. 1 coulomb
c. 1 faraday
d. None of the above
Answer : C

Question. The conductivity of strong electrolyte is:
a. Increase on dilution slightly
b. Decrease on dilution
c. Does not change with dilution
d. Depend upon density of electrolytes itself
Answer : A

Question. If equivalent conductance of 1M benzoic acid is 12.8ohm⁻¹ cm²  and if the conductance of benzoate ion and H⁺ ion are 42 and 288.42 ohm¹ cm² − respectively. Its degree of dissociation is:
a. 39%
b. 3.9%
c. 0.35%
d. 0.039%
Answer : B

Question. The unit ohm⁻¹ is used for:
a. Molar conductivity
b. Equivalent conductivity
c. Specific conductivity
d. Conductivity
Cell Constant and Electrochemical Cell
Answer : D

Question. If the Zn / Zn²⁺ electrode is diluted to 100 times then the change in e.m.f.:
a. Increase of 59mV
b. Decrease of 59mV
c. Increase of 29.5mV
d. Decrease of 29.5mV
Answer : A

Question. The tendency of an electrode to lose electrons is known as:
a. Electrode potential
b. Reduction potential
c. Oxidation potential
d. e.m.f.
Answer : C

Question. In the cell Zn | Zn²⁺ || Cu²⁺ | Cu, the negative electrode is:
a. Cu
b. Cu²⁺
c. Zn
d. Zn²⁺
Answer : C

Question. The specific conductance of a 0.1 N KCl solution at 23^oC is 0.012ohm⁻¹ cm⁻¹ The resistance of cell containing the solution at the same temperature was found to be 55 ohm. The cell constant will be:
a. 0.142cm⁻¹
b. 0.66cm⁻¹
c. 0.918cm⁻¹
d. 1.12cm⁻¹
Answer : B

Question. When lead storage battery is charged?
a. Lead dioxide dissolves
b. Sulphuric acid is regenerated
c. The lead electrode becomes coated with lead sulphate
d. The amount of sulphuric acid decreases
Answer : B

Question. At 25°C specific conductivity of a normal solution of KCl is 0.002765 mho. The resistance of cell is 400 ohms. The cell constant is:
a. 0.815
b. 1.016
c. 1.106
d. 2.016
Answer : C

Question. In a hydrogen– oxygen fuel cell, combustion of hydrogen occurs to:
a. Produce high purity water
b. Create potential difference between the two electrodes
c. Generate heat
d. Remove adsorbed oxygen from electrode surfaces
Answer : B

Question. In electrolysis of dilute H₂SO₄ using platinum electrodes:
a. H₂ is evolved at cathode
b. NH₃ is produced at anode
c. Cl₂ is obtained at cathode
d. O₂ is produced
Answer : A

Question. If hydrogen electrode dipped in 2 solution of pH = 3 and pH = 6 and salt bridge is connected the e.m.f. of resulting cell is:
a. 0.177 V
b. 0.3 V
c. 0.052 V
d. 0.104 V
Answer : A

Question. If a strip of Cu metal is placed in a solution of ferrous sulphate:
a. Copper will precipitate out
b. Iron will precipitate out
c. Copper will dissolve
d. No reaction will take place
Answer : D

Short Answer Type Questions

Question. Kailash goes to the market to purchase battery for his car. Two types of batteries are shown to him, one with cadmium plates which is relatively more costlier while the other one with lead plates which is cheaper. The shopkeeper advises him to go for cadmium plate battery instead of lead plate battery.
Answer the following questions:
(i) As a chemistry student, do you agree with shopkeeper’s advise?
(ii) Give two reasons to support his advise.
(iii) What are the values associated with his advise?
Answer:
(i) Yes, shopkeeper is right to advise him to purchase cadmium plate battery.
(ii) It is wise to choose sustained long-term benefit than short-term gain with regards to health/money. Lead produces harmful effects on human beings and environment.
(iii) Knowledge is useful only when put into practice. Knowledge of harmful effects of lead make us aware of less usage of lead batteries and also unleaded petrol to keep ourselves and our environment healthy.

Question. During the construction of some public building, the contractor intends to fix iron frames for windows and railings to reduce the cost of construction. After due considerations, it is finally recommended to use aluminium frames for windows and steel railings instead of iron.
Answer the following questions:
(i) As a chemist, do you agree with the new recommendations.
(ii) Give two reasons for your choice.
(iii) What values are associated with the decision?
Answer:
(i) Yes, the new recommendations are more appropriate in the light of long-term benefit.
(ii) Iron grills and railings are more prone to corrosion which causes damage to the construction gradually. Aluminium and steel are relatively safer in this respect.
(iii) Knowledge of corrosion/rusting of iron and its prevention makes us aware of its proper application in construction work so as to avoid damage and accidents.

Question. In earlier days food items and products like cooking oil, sugar and biscuits were packed in tin containers. These containers were then used by housewives for storing grains and other kitchen items. Now exports /imports in tin containers are strictly prohibited; in spite of this we still seem to permit the tin containers for soft drinks.
a) What do you think is the reason for the prohibition?
b) Should we continue to use soft drink cans?
c) What values do we lack based on this information? 
Answer:
(a) Tin is a metal that can easily corrode when exposed to atmosphere. This can spoil the food item stored in it.
(b) No, because soft drinks are highly acidic and std reduction potential of tin is lesser than hydrogen and hence it can react with acidic component of the drink.
(c) Lack of awareness about harmful effects of harmful metals on our health, getting highly influenced by advertisements.

Question. Two iron plates, with dents were allotted to two students for plating and study of prevention of rusting. The first student selected tin for coating his plate, while the second chose zinc for the same purpose.
a) Who do you think made the right choice, and why?
b) Mention one value associated with the study of corrosion.
Answer:
(a) The student who chose zinc, made the right choice. Zinc is more reactive than iron and hence its coating can prevent corrosion of iron.
(b) Ability to apply gained knowledge in day to day activities.

Question. Raju and his father were going in a boat in the river. Raju’s father threw away the cell used in watches and hearing aids into the water. Raju prevented him from doing so.
a. As a student of chemistry, why would you advise Raju’s father not to throw the cell in the water body.
b. What is the value associated with the above decision?
Answer:
a. The cells used in watches are mercury cells. The mercury can pollute water. Water contaminated with mercury leads to accumulation of mercury in the body of the fishes and other aquatic life.
b. Keeping the environment safe from pollution due to mercury.

Question. The water pipe line of a house has started rusting. The lady of the house does not want excavation of the pipelines. As a student of chemistry what would you suggest her to do so that further rusting can be prevented? What values are shown by you in this gesture?
Answer: 
Magnesium block should be attached to water pipeline through an electric wire. It will act as anode and undergo oxidation in preference to iron (Cathodic protection) Values: Helping mentality shown towards needy people, application of learnt knowledge in day to day activities, ability to make complicated work simple.

Please refer to the link below for CBSE Class 12 Chemistry - Electrochemistry VBQs