Question

The standard electrode potential $\left(E^{\circ}\right)$ for $OCl ^{-} / Cl ^{-}$ and $-\frac{1}{2} Cl _{2}$ respectively are $0.94\, V$ and $-1.36\, V$. The $E^{\circ}$value for $OCl ^{-} / \frac{1}{2} Cl _{2}$ will be

• A. -0.42 V
• B. -2.20 V
• C. 0.52 V
• D. 1.04 V

Answer 1

Answer: (C)

The given half cell reactions can be written as

(i) $OCl ^{-}+ H _{2} O +2 e^{-} \rightarrow Cl ^{-}+2 OH \,\,\, E_{1}^{\circ}=0.94\, V$

(ii) $Cl ^{-} \rightarrow \frac{1}{2} Cl _{2}+e^{-}\,\,\,E_{2}^{\circ}=-1.36\, V$

(iii) $OCl ^{-}+ H _{2} O +e^{-} \rightarrow \frac{1}{2} Cl _{2}+2 OH ;\,\,\, E_{3}^{\circ}=?$

Now consider free energies $\left(\Delta G^{\circ}=-n E^{\circ} F\right)$

$\Delta G_{3}^{\circ}=\Delta G_{1}^{\circ}+\Delta G_{2}^{\circ}$

or $-1 \times F \times E_{3}^{\circ}=-2 \times F(0.94)-1 \times F(-1.36)$

or $E_{3}^{\circ}=2 \times 0.94-1.36=0.52\, V$