Question

At $25℃$, the dissociation constant of a base, $BOH$ is $1.0\times {10}^{-12}$. The concentration of hydroxyl ions in $0.01M$ aqueous solution of the base would be:

• A. $2.0\times {10}^{-6}mol{L}^{-1}$
• B. $1.0\times {10}^{-5}mol{L}^{-1}$
• C. $1.0\times {10}^{-6}mol{L}^{-1}$
• D. $1.0\times {10}^{-7}mol{L}^{-1}$

Answer 1

The correct option is D $1.0\times {10}^{-7}mol{L}^{-1}$

$BOH\rightleftharpoons B^{+}+{OH}^{-}$

$K_b=\frac{\left[B^{+}\right]\left[{OH}^{-}\right]}{\left[BOH\right]}$

$\therefore 1\times {10}^{-12}=\frac{{\left[{OH}^{-}\right]}^2}{0.01}$ $(\because$ $\left[{OH}^{-}\right]=\left[B^{+}\right])$

$\therefore {\left[{OH}^{-}\right]}^2={10}^{-14}\therefore \left[{OH}^{-}\right]={10}^{-7}M\Rightarrow 1\times {10}^{-7}mol{L}^{-1}$

Answer:$\left(D\right)1.0\times {10}^{-7}mol{L}^{-1}$