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Electrochemistry

Short Answer Type

161. Zinc rod is dipped in 0.1 M solution of ZnSO₄. The salt is 95% dissociated at this dilution at 298 K. Calculate the electrode potential. [Given that: E°_Zn²⁺/Zn = – 0.76 V.]

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162.

Calculate the equilibrium constant for the reaction,
Cu(s) + 2Ag⁺ (aq) → Cu²⁺ (aq) + 2Ag(s)
[E°_cell = 0.46 V]
(T = 298 K, F = 96500 C mol^–1, R = 8.31 J K^–1 mol^–1)

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163. Calculate the resistance offered by 0.5 M CH₃COOH solution when its molar conductivity. is 7.4 Ω^–1 cm² mol^–1 and the cell constant is 0.037 cm^–1.

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Long Answer Type

164. A 0.05 M NaOH solution offered a resistance of 31.6 Ω in a conductivity cell is 0.367 cm^–1, find out the specific and molar conductance of the sodium hydroxide solution.

(i) Resistance (k) = $3.16 Ω$
Conductance (C) = $\frac{1}{R}$
= $\frac{1}{3.16 ohm} = 0.0316 {ohm}^{- 1}$
Specific conductance (k)
= Conductance x cell constant
$= 0.0316 {ohm}^{- 1} \times 0.367 {cm}^{- 1} = 0.0116 {ohm}^{-} {cm}^{- 1}$
(ii) Molar conductance (C)
$= 0.05 M = 0.05 mol L^{- 1} = \frac{0.05 mol}{1 L} = \frac{0.05 mol}{10^{3} {cm}^{3}} = 0.05 \times 10^{- 3} mol {cm}^{- 3}$
Molar conductance $(Λ_{m})$
$= \frac{k}{C} = \frac{(0.0116 {ohm}^{- 1} {cm}^{- 1})}{(0.05 \times 10^{- 3} mol {cm}^{- 3})} = 232 {ohm}^{- 1} {cm}^{2} {mol}^{- 1} .$

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165. Calculate the maximum possible electric work that can be obtained from the following cell under the standard conditions at 25°C:

Fe | {Fe}^{2 +} (aq) | | {Cu}^{2 +} (aq) | Cu

E °_{{Fe}^{2 +} (aq) / Fe} = - 0.44 V E °_{{Cu}^{2 +} (aq) / Cu} = + 0.34 V and F = 96, 500 C .

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166. Zn | Zn²⁺ (α = 0.1 M) || Fe²⁺ (α = 0.01 M) | Fe. The emf of the above cell is 0.2905 V. What is the equilibrium constant for the cell reaction?

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167. When a certain conductivity cell was filled with 0.1 M KCl, it has a resistance of 85 Q at 25°C. When the same cell was filled with an aqueous solution of 0.052 M unknown electrolyte, the resistance was 96 Ω. Calculate the molar conductivity of the unknown electrolyte at this concentration. (Specific conductivity of 0.1 M KCl = 1.29 x 10^–2 ohm^–1cm^–1).

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168. In a fuel cell, H₂ and O₂ react to produce electricity. In the process H₂ gas is oxidised at the anode and O₂ at cathode. If 67.2 litre of H₂ at STP reacts in 15 minutes, what is the average current produced? If the entire current is used for electro-deposition of Cu from Cu²⁺, how many grams of copper are deposited?

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169.

The following electrochemical cell has been set up
Pt(1) | Fe³⁺, Fe²⁺ (a = 1) || Ce⁴⁺, Ce³⁺ (a = 1) | Pt (2)
E°_(Fe²⁺) = 0.77 V, and E°_{(Ce⁴⁺,Ce³⁺)} = 1.61 V
If an ammeter is connected between the two platinum electrodes, predict the direction of flow of current. Will the current increase or decrease with time?

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Short Answer Type

170. How many grams of silver could be placed out on a shild by electrolysis of a solution containing Λ° ions for a period of 4 hours by a current strength of 8.5 amperes? [F = 96,500 C mol^–1, Molar mass of Ag = 107.8 g]

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