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Electrochemistry

Multiple Choice Questions

91.

The standard electrode potentials of Zn and Ni respectively are - 0.76 V and - 0.25 V. Then the standard emf of the spontaneous cell by coupling these under standard conditions is

+1.01 V
-0.51 V
+0.51 V
+0.25 V

92.

How many moles of platinum will be deposited on the cathode when 0.60 F of electricity is passed through a 1.0 M solution of Pt⁴⁺?

0.60 mol
0.15 mol
0.30 mol
0.45 mol

93.

A 250 W electric bulb of 80% efficiency emits a light of 6626 Å wavelength. The number of photons emitted per second by the lamp is (h = 6.636 x 10^-34Js)

1.42 × 10¹⁷
2.18 × 10¹⁶
6.66 × 10²⁰
2.83 × 10¹⁶

94.
Consider the following elecrolytic cells
(i) M (s) | M²⁺ (aq), 0.1 M || X²⁺ (aq), 0.01 M | X (s)
(ii) M (s) | M²⁺ (aq), 0.1 M || X² (aq), 0.01 M | X (s)
(iii) M (s) | M²⁺ (aq), 0.1 M || X² (aq), 0.01 M | X (s)
The cell EMF of the above cells are E₁, E₂ and E₃ respectively. Which one of the following is true?

E₃ > E₂ > E₁

E₁ > E₂ > E₃

E₂ > E₃ > E₁

E₁ > E₃ > E₂

E₃ > E₂ > E₁

For the given cell, cell reaction is

M + X²⁺ → M²⁺ + X

Nernst equation is

E = E° - $\frac{0.059}{2} \log \frac{[M^{2 +}]}{[X^{2 +}]}$

= E° + $\frac{0.059}{2} \log \frac{[X^{2 +}]}{[M^{2 +}]}$

For cell (i),

$E_{1} = E ° + \frac{0.059}{2} \log \frac{(0.01)}{(0.1)} = E ° + \frac{0.059}{2} (- 1) = E ° - \frac{0.059}{2} E_{2} = E ° + \frac{0.059}{2} \log \frac{(0.1)}{(0.1)} = E ° + \frac{0.059}{2} \log 1 = E ° (∵ \log 1 = 0) E_{3} = E ° + \frac{0.059}{2} \log \frac{(0.1)}{(0.01)} = E ° + \frac{0.059}{2} \log 10 = E ° + \frac{0.059}{2}$

Thus, the order of E₁, E₂ and E₃ is

E₃ > E₂ > E₁

95.

When the total cell emf of a volatic cell is greater than zero, which of the following is true about the reaction quotient Q and free energy change $∆$ G for the cell reaction?

Q is less than one and $∆$ G is greater than zero
Q is greater than one and $∆$ G is greater than zero
Q is greater than one and $∆$ G is less than zero
Q is zero and $∆$ G is greater than zero

96.

In dry cell, what acts as a negative electrode?

Zinc
Graphite
Ammonium chloride
Manganese dioxide

97.

A weak electrolyte having the limiting equivalent conductance of 400 S cm² g equiv^-1 at 298 K is 2% ionized in its 0.1 N solution. The resistance of this solution (in ohm) in an electrolytic cell of cell constant 0.4 cm^-1 at this temperature is

98.

Given that the standard reduction potentials for M⁺/ M and N⁺ / N electrodes at 298 K are 0.52 V and 0.25 V respectively. Which of the following is correct in respect of the following electrochemical cell?

M | M⁺ || N⁺ | N

The overall cell reaction is a spontaneous reaction
The standard EMF of the cell is -0.27 V
The standard EMF of the cell is 0.77 V
The standard EMF of the cell is -0.77 V

99.

The standard redox potential for the reactions, Mn²⁺ + 2e^- → Mn and Mn³⁺ + e^- → Mn²⁺ are -1.18 V and 1.51 V respectively. What is the redox potential for the reaction Mn³⁺ + 3e^- → Mn?

0.33 V
1.69 V
- 0.28 V
-0.85 V

100.

The limiting molar conductivities of HCl, CH₃COONa and NaCl are respectively 425, 90 and 125 mho cm² mol^-1 at 25°C. The molar conductivity of 0.1 M CH₃COOH solution is 7.8 mho cm² mol^-1 at the same temperature. The degree of dissociation of 0.1 M acetic acid solution at the same temperature is

0.10
0.02
0.15
0.03