Question

pH of ${10}^{-8}$N NaOH is?

• A. $8.0$
• B. $6.0$
• C. $6.98$
• D. $7.04$

Answer 1

The correct option is D $7.04$

$\because \left[NaOH\right]={10}^{-8}M$

$\therefore \left[O{H}^{-}\right]=1\times {10}^{-8}M$

Here, $\left[O{H}^{-}\right]$ of water in this dilute solution should be added.

$\therefore [O{H}^{-}{]}_{Total}$ $=\underset{H_{2}Oapprox.}{\underset{}{1\times {10}^{-7}M}}+\underset{NaOH}{\underset{}{1\times {10}^{-8}M}}$ $=11\times {10}^{-8}M$

$\therefore pOH=-log\left[O{H}^{-}\right]=8-log11=8-1.04=6.96$

$pH=14-pOH=14-6.96=7.04$.