The two half-cell reactions of an electrochemical cell is given as

$$\begin{gathered} {\mathrm{Ag}}^{+} + {\mathrm{e}}^{-} \to \mathrm{Ag}; \mathrm{E}{°}_{{\mathrm{Ag}}^{+}/\mathrm{Ag}}=-0.3995 \mathrm{V} \\ {\mathrm{Fe}}^{2+}\to {\mathrm{Fe}}^{3+} + {\mathrm{e}}^{-} ; \mathrm{E}{°}_{{\mathrm{Fe}}^{3+} /{\mathrm{Fe}}^{2+}}= -0.7120 \mathrm{V} \end{gathered}$$

The value of cell EMF will be

• -0.3125 V

• 0.3125 V

• 1.114 V

• -1.114V

42.

At 25C, the molar conductance of 0.007 M hydrofluoric acid is 150 mho cm²mol^-1and its $\mathrm{\lambda }{°}_{\mathrm{m}}$ = 500 mho cm²mol^-1. The value of the dissociation constant of the acid at the given concentration at 25°C is

• 7 X 10^-4 M

• 7 X 10^-5 M

• 9 X 10^-3 M

• 9 X 10^-4 M

The formal potential of Fe³⁺ /Fe⁴⁺ in a sulphuric acid and phosphoric acid mixture (E° = + 0.61 V) is much lower than the standard potential (E° = + 0. 77 V). This is due to

• formation of the species [FeHPO₄]⁺

• lowering of potential upon complexation

• formation of the species [FeSO₄]⁺

• high acidity of the medium

A conductivity cell has been calibrated with a 0.01 M 1 : 1 electrolyte solution (specific conductance, k = 1.25 × 10^-3S cm^-1) in the cell and the measured resistance was 800 $\Omega$ at 25°C. The cell constant will be

• 1.02 cm^-1

• 0.102 cm^-1

• 1.00 cm^-1

• 0.5 cm^-1

Equivalent conductivity at infinite dilution for sodium-potassium oxalate [(COO^-)₂ Na⁺K⁺] will be [given molar conductivities of oxalate, K⁺ and Na⁺ ions at infinite dilution are 148.2, 50.1, 73.5 S cm mol' respectively]

• 271.8 S cm² eq^-1

• 67.95 S cm² eq^-1

• 543.6 S cm² eq^-1

• 135.9 S cm² eq^-1

The standard reduction potential E° for half-reaction are

Zn → Zn²⁺ + 2e^- ; E° = + 0.76 V

 Fe → Fe²⁺ + 2e^- ; E° = + 0.41 V

The EMF of the cell reaction

Fe²⁺ + Zn → Zn²⁺ + Fe is

• -0.35 V

• +0.35 V

• +1.17 V

• -1.17 V

On passing 'C ampere of current for time 't' sec through 1 L of 2 (M) CuSO₄ solution (atomic weight of Cu= 63. 5), the amount 'm' of Cu (in gram) deposited on cathode will be

• m = Ct / (63.5 x 96500)

• m = Ct / (31.25 x 96500)

• m = (C x 96500) / (31.25xt)

• m = (31.25 X C x t) / 96500

When 96.5 C of electricity is passed through a solution of silver nitrate (at wt. of Ag = 107. 8 7 which is approx. 108), the amount of silver deposted is

• 5.8 mg

• 10.8 mg

• 15.8 mg

• 20.8 mg

The standard reduction potentials at 298 K for the following half reactions are given against each

                          $$\begin{gathered} {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Zn}\left(\mathrm{s}\right) -0.762 \mathrm{V} \\ {\mathrm{Cr}}^{3+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Cr}\left(\mathrm{s}\right) - 0.740 \mathrm{V} \\ 2{\mathrm{H}}^{+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons {\mathrm{H}}_2\left(\mathrm{s}\right) 0.000 \mathrm{V} \\ {\mathrm{Fe}}^{3+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons {\mathrm{Fe}}^{2+}\left(\mathrm{aq}\right) 0.770 \mathrm{V} \end{gathered}$$

Which is the strongest reducing agent ?

• Zn(s)

• Cr(s)

• H₂(s)

• Fe²⁺ (aq)

On passing 3A of electricity for 50 min, 1.8 g metal is deposited, the equivalent mass of metal is

• 9.3

• 19.3

• 38.3

• 39.9