Question

A weak mono acidic base is $5$% ionized in $0.01M$ solution. The hydroxide ion concentration in the solution is:

• A. $5\times {10}^{-2}$
• B. $5\times {10}^{-4}$
• C. $5\times {10}^{-10}$
• D. $2\times {10}^{-11}$

Answer 1

Answer: (B)

$5\times {10}^{-4}$

Let the monoacidic base be $BOH$.

Given that $c=0.01M$ and $\alpha =0.05$.

SInce $\alpha \ll 1$

On dissociation,
$BOH\leftrightharpoons B^{+}+O{H}^{-}$

$c$ $-$ $-$
$c(1-\alpha )$ $c\alpha$ $c\alpha$

The concentration of $O{H}^{-}$ is given by $c\alpha$.

$\Rightarrow \left[O{H}^{-}\right]=0.01\times 0.05$

$\Rightarrow \left[O{H}^{-}\right]=5\times {10}^{-4}$.

Hence, option B is correct.