Question

Monoacidic weak base $MOH$ has the dissociation constant value as $1.8\times {10}^{-5}$. What would be the concentration of $O{H}^{-}$ in its 0.1 M solution :

• A. $1.8\times {10}^{-5}$
• B. $1.34\times {10}^{-3}M$
• C. $5\times {10}^{-5}M$
• D. $4.0\times {10}^{-3}M$

Answer 1

The correct option is B $1.34\times {10}^{-3}M$

For a monoacidic weak base $MOH$, the relationship between the hydroxide concentration, the base concentration $C$ and the dissociation constant $K_b$ is

$\left[O{H}^{-}\right]=\sqrt{K_{b}C}=\sqrt{1.8\times {10}^{-5}\times 0.1}=1.34\times {10}^{-3}M$