Electrochemistry 2 Question 47
46. Zinc granules are added in excess to a $500 \mathrm{~mL}$ of $1.0 \mathrm{M}$ 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 $-0.75 \mathrm{~V}$ and $-0.24 \mathrm{Vrespectively.} \mathrm{Find} \mathrm{out} \mathrm{the}$ concentration of $\mathrm{Ni}^{2+}$ in solution at equilibrium.
$(1991,2 M)$
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Solution:
- The redox reaction is
$$ \begin{array}{cc} & \mathrm{Zn}+\mathrm{Ni}^{2+} \rightleftharpoons \mathrm{Zn}^{2+}+\mathrm{Ni} \quad E^{\circ}=+0.51 \mathrm{~V} \ \Rightarrow & E^{\circ}=\frac{0.0592}{2} \log K \ \Rightarrow & \log K=\frac{0.51 \times 2}{0.0592}=17.23 \ \Rightarrow & K=1.7 \times 10^{17} \end{array} $$
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. $1.0 \mathrm{M}$.
