Electrochemistry Result Question 46
46. Zinc granules are added in excess to a 500 mL of 1.0 M nickel nitrate solution at $25^{\circ} \mathrm{C}$ until the equilibrium is reached. If the standard reduction potential of $\mathrm{Zn}^{2+} / \mathrm{Zn}$ and $\mathrm{Ni}^{2+} / \mathrm{Ni}$ are -0.75 V and -0.24 Vrespectively. Find out the concentration of $\mathrm{Ni}^{2+}$ in solution at equilibrium.
(1991, 2M)
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Answer:
Correct Answer: 46. $(1.7 \times 10^{17})$
Solution:
- The redox reaction is
$ \mathrm{Zn}+\mathrm{Ni}^{2+} \rightleftharpoons \mathrm{Zn}^{2+}+\mathrm{Ni} \quad E^{\circ}=+0.51 \mathrm{~V} $
$\Rightarrow E^{\circ}=\frac{0.0592}{2} \log K $
$\Rightarrow \log K =\frac{0.51 \times 2}{0.0592}=17.23 $
$\Rightarrow K =1.7 \times 10^{17}$
Such a high value of equilibrium constant indicates that the reaction is almost complete. Therefore, concentration of $\mathrm{Zn}^{2+}$ in solution will be equal to initial concentration of $\mathrm{Ni}^{2+}$ ion, i.e. $1.0$ $ M$ .
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