Find out the solubility of Ni(OH)_2 in 0.1 M NaOH. Given that the ionic product of Ni(OH)_2 is 2×10^-15.
1. \(2\times10^{-13}\) M
2. \(2\times10^{-8}\) M
3. \(1\times10^{-13}\) M
4. \(1\times10^{8}\) M
1. \(2\times10^{-13}\) M
2. \(2\times10^{-8}\) M
3. \(1\times10^{-13}\) M
4. \(1\times10^{8}\) M
Best answer
Answer: 1. \(2\times10^{-13}\) M
In 0.1 M NaOH the common ion \(\mathrm{OH^-}\) is already present, so the \(\mathrm{OH^-}\) from \(\mathrm{Ni(OH)_2}\) can be ignored.
\(\mathrm{Ni(OH)_2 \rightleftharpoons Ni^{2+} + 2OH^-}\), \(K_{sp}=[\mathrm{Ni^{2+}}][\mathrm{OH^-}]^2\).
Let solubility be \(s\): \(s=[\mathrm{Ni^{2+}}]\), \([\mathrm{OH^-}]\approx0.1\) M.
$$s=\frac{K_{sp}}{(0.1)^2}=\frac{2\times10^{-15}}{10^{-2}}=2\times10^{-13}\ \mathrm{M}$$
Option (1) is correct.
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