Q12 / 160 · TS EAMCET 2017 · Chemistry

Consider the single electrode process $4 \mathrm{H}^{+}+4 \mathrm{e}^{-} \rightleftharpoons 2 \mathrm{H}_2$ catalysed by platinum black electrode in $\mathrm{HCl}$ electrolyte. The potential of the electrode is $-0.059 \mathrm{~V}$. SHE. What is the concentration of the acid in the hydrogen half cell if the $\mathrm{H}_2$ pressure is $1 \mathrm{bar}$ ? $$ 4 \mathrm{H}^{+}+4 e^{-} \rightleftharpoons 2 \mathrm{H}_2 $$

  • A
    $1 \mathrm{M}$
  • B
    $10 \mathrm{M}$
  • Correct answer
    C
    $0.1 \mathrm{M}$
  • D
    $0.01 \mathrm{M}$

Solution

$4 \mathrm{H}^{+}+4 \mathrm{e}^{-} \rightleftharpoons 2 \mathrm{H}_2$ $$ \begin{aligned} & E=E^{\circ}-\frac{0.059}{n} \log \frac{p \mathrm{H}_2}{\left[\mathrm{H}^{+}\right]^4} \\ & -0.059=0-\frac{0.059}{4} \log \frac{1}{\left[\mathrm{H}^{+}\right]^4} \\ & =\left[\mathrm{H}^{+}\right]=10^{-1}=0.1 \mathrm{M} \end{aligned} $$

Hence, the correct answer is option: 'C'.

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