${\mathrm{E}}_{\mathrm{cell}}^{\circ }$ for the given redox reaction is 2.71 V
Mg(s) + Cu²⁺ (0.01 M) –––→ Mg²⁺ (0.001 M) + Cu(s)
Calculate E_cell for the reaction. Write the direction of flow of current when an external opposite potential applied is
(i) less than 2.71 V and
(ii) greater than 2.71 V

OR

(a) A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO₄ and ZnSO₄ until 2.8 g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y. (Molar mass: Fe = 56 g mol^–1 Zn = 65.3 g mol^–1, 1F = 96500 C mol^–1)

(b) In the plot of molar conductivity (𝛬_m) vs square root of concentration (c^1/2), following curves are obtained for two electrolytes A and B

$\begin{array}{l}{\mathrm{E}}_{\text{cell }}={\mathrm{E}}_{\text{cell }}^{\circ }-\frac{0.059}{\mathrm{n}}\log {\mathrm{K}}_{\mathrm{c}}\\ =2.71-\frac{0.059}{2}\log \frac{{10}^{-3}}{{10}^{-2}}\\ =2.71+0.0295\\ {\mathrm{E}}_{\text{cell }}=2.7395\mathrm{V}\\ \end{array}$
(i) When an external opposite potential of less than 2.71 V is applied the current will flow in same direction from cathode to anode.
(ii) When an external opposite potential of more than 2.71 V is applied the current will flow in opposite direction from anode to cathode.

OR

(a) I =2 Ampere
56 g of Fe requires =2× 96500 C
$\therefore 2.8 \mathrm{g}\text{ will require }=2.8\times \frac{2\times 96500}{56}=9650 \mathrm{C}$
$\begin{array}{l}\mathrm{Q}=\mathrm{It}\\ \mathrm{t}=\frac{\mathrm{Q}}{\mathrm{I}}=\frac{9650}{2}=4825 \mathrm{s}\end{array}$
Using Faraday's second law of electrolysis
$\frac{{\mathrm{w}}_1}{{\mathrm{w}}_2}=\frac{{\mathrm{E}}_1}{{\mathrm{E}}_2}$
Where w₁ = mass of Fe and w₂= mass of Zn
$\begin{array}{l}\frac{2.8}{{\mathrm{w}}_2}=\frac{56}{2}\times \frac{2}{65.3}\\ {\mathrm{w}}_2=3.265\mathrm{g}\end{array}$
(b) (i) A is a strong electrolyte and B is a weak electrolyte. 

(ii) For B, 𝛬_m value at zero concentration cannot be obtained by extrapolation as it is a weak electrolyte. For A, the intercept will give the 𝛬_m value at zero concentration.