Question

$K_b$ for a monoacidic base whose $0.1M$ solution has a $pH$ of $10.50$ is:

• A. $K_b={10}^{-3}$
• B. $K_b={10}^{-6}$
• C. $K_b={10}^{-9}$
• D. None of these

Answer 1

Answer: (B)

$K_b={10}^{-6}$

$pH=-log\left[H^{+}\right]=10.5$

$pOH=14-pH=3.5$

Also, for a mono-acidic base $\left[O{H}^{-}\right]=c\times \alpha$

$K_b=c\times {\alpha }^2=\frac{[O{H}^{-}{]}^2}{C}$

So by putting value of $C=0.1M$, we get

$K_b={10}^{-6}$