Question

An aqueous solution contains $0.01$M $RN{H}_2$ ($K_b=2\times {10}^{-6}$) & ${10}^{-4}$M NaOH. The concentration of $O{H}^{-}$ is nearly.

Answer 1

${RNH}_2$ is a weak base. It will react with $H_{2}O$ is generated ${OH}^{(-)}$ ions.

$\left[{OH}^{(-)}\right]=\sqrt{K_c\times C}+\left[NaOH\right]$

$=\sqrt{2\times {10}^{-6}\times {10}^{-2}}+{10}^{-4}$

$=1.41\times {10}^{-4}+{10}^{-4}$

$=2.41\times {10}^{-4}M$