Electrochemistry — Class 12 Chemistry PYQs

The unit of cell constant is :
(A) ohm cm⁻¹
(B) ohm⁻¹
(C) cm⁻¹
(D) ohm⁻¹ cm² mol⁻¹

During electrolysis of aqueous CuCl₂ :
(A) H₂ (g) is liberated at cathode
(B) Cu is formed at cathode
(C) O₂ (g) is liberated at anode
(D) Cl₂ (g) is liberated at cathode

During electrolysis of aqueous solution of NaCl :
(A) H₂ (g) is liberated at cathode
(B) Na is formed at cathode
(C) O₂ (g) is liberated at anode
(D) Cl₂ (g) is liberated at cathode

Calculate the potential of Iron electrode in which the concentration of Fe²⁺ ion is 0.01 M.

Given : E°(Fe²⁺/Fe) = −0.45 V at 298 K

[log 10 = 1]

When a certain conductivity cell was filled with 0.05 M KCl solution, it has a resistance of 100 ohm at 25°C. When the same cell was filled with 0.02 M AgNO₃ solution, the resistance was 90 ohm.

Calculate the conductivity and molar conductivity of AgNO₃ solution.

(Given : Conductivity of 0.05 M KCl solution = 1.35 × 10⁻² ohm⁻¹ cm⁻¹)

Calculate emf of the following cell :

$$\text{Zn(s)}\mid {\text{Zn}}^{2+}(0.1\text{ M})\mid \mid {\text{Sn}}^{2+}(0.001\text{ M})\mid \text{Sn(s)}$$

Given : E°(Zn²⁺/Zn) = −0.76 V, E°(Sn²⁺/Sn) = −0.14 V

[log 10 = 1]

Batteries and fuel cells are very useful forms of galvanic cell. Any battery or cell that we use as a source of electrical energy is basically a galvanic cell. However, for a battery to be of practical use it should be reasonably light, compact and its voltage should not vary appreciably during its use. There are mainly two types of batteries — primary batteries and secondary batteries.

In the primary batteries, the reaction occurs only once and after use over a period of time the battery becomes dead and cannot be reused again, whereas the secondary batteries are rechargeable.

Production of electricity by thermal plants is not a very efficient method and is a major source of pollution. To solve this problem, galvanic cells are designed in such a way that energy of combustion of fuels is directly converted into electrical energy, and these are known as fuel cells. One such fuel cell was used in the Apollo space programme.

Answer the following questions :

(a) How do primary batteries differ from secondary batteries ?

(b) The cell potential of Mercury cell is 1.35 V, and remains constant during its life. Give reason.

(c) Write the reactions involved in the recharging of the lead storage battery.

OR

(c) Write two advantages of fuel cells over other galvanic cells.

(a) (i) The resistance of 0.05 M CH₃COOH solution is found to be 100 ohm. If the cell constant is 0.0354 cm⁻¹, calculate the molar conductivity of the acetic acid solution.

(ii) State Faraday's first law of electrolysis. How much charge in Faraday is required for the reduction of 1 mol of MnO₄⁻ to Mn²⁺ ?

OR

(b) (i) The conductivity of 0.0025 mol L⁻¹ acetic acid is 5.25 × 10⁻⁵ S cm⁻¹. Calculate its degree of dissociation if Λ°ₘ for acetic acid is 390 S cm² mol⁻¹.

(ii) Write anode, cathode and overall reaction of lead storage battery.

Calculate the potential of Iron electrode in which the concentration of Fe²⁺ ion is 0.01 M.
(E° Fe²⁺/Fe = – 0.45 V at 298 K)
[Given : log 10 = 1]

During electrolysis of aqueous solution of NaCl :