ElectrochemistryHard

Question

The dissociation constant for CH3COOH is 1.8 × 10−5 at 298 K. The electrode potential for the half-cell:

Pt|H2 (1 bar)|0.5 M – CH3COOH, at 298 K is (log 2 = 0.3; log 3 = 0.48; 2.303 RT/F = 0.06)

Options

A.−0.3024 V
B.−0.1512 V
C.+0.3024 V
D.+0.1512 V

Solution

$H_{2}(g) \rightleftharpoons 2H(aq) + 2e^{-}$

$E_{H_{2}|CH_{3}COOH} = E_{H_{2}|H^{+}} = E_{H_{2}|H^{+}}^{o} - \frac{0.06}{2}.\log\frac{\left( H^{+} \right)^{2}}{P_{H_{2}}}$

$= 0 - \frac{0.06}{2}.\log\frac{\left( \sqrt{Ka \times C} \right)^{2}}{P_{H_{2}}} $$$= - \frac{0.06}{2}.\log\frac{1.8 \times 10^{- 5} \times 0.5}{1} = + 0.1512\text{ V}$$

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