Electrochemistry 2 Question 34
33. When ammonia is added to the solution, $\mathrm{pH}$ is raised to 11 . Which half-cell reaction is affected by $\mathrm{pH}$ and by how much?
(a) $E_{\text {oxi }}$ will increase by a factor of 0.65 from $E_{\text {oxi }}^{\circ}$
(b) $E_{\text {oxi }}$ will decrease by a factor of 0.65 from $E_{\text {oxi }}$
(c) $E_{\text {red }}$ will increase by a factor of 0.65 from $E_{\text {red }}^{\circ \times 1}$
(d) $E_{\text {red }}$ will decrease by a factor of 0.65 from $E_{\text {red }}^{\circ}$
Show Answer
Solution:
- On increasing concentration of $\mathrm{NH}_{3}$, the concentration of $\mathrm{H}^{+}$ion decreases, therefore,
$$ \begin{aligned} E_{\text {red }} & =E_{\text {red }}^{\circ}-\frac{0.0592}{2} \log \left[\mathrm{H}^{+}\right]^{2}=0-\frac{0.0592}{2} \times 2 \log 10^{-11} \ & =0.65 \mathrm{~V} \end{aligned} $$
i.e. $E_{\text {red }}$ increases by $0.65 \mathrm{~V}$.
