Question

pH of the solution is 3. The hydroxide ion concentration of the solution would be:

• A. ${10}^{-4}$
• B. ${10}^{-10}$
• C. ${10}^{-11}$
• D. ${10}^{-3}$

Answer 1

The correct option is C ${10}^{-11}$

$pH=-log\left[H^{+}\right]=3$.
Thus $\left[H^{+}\right]={10}^{-3}$.
But $\left[H^{+}\right]\left[O{H}^{-}\right]={10}^{-14}$.
$\left[O{H}^{-}\right]=\frac{{10}^{-14}}{\left[H^{+}\right]}=\frac{{10}^{-14}}{{10}^{-3}}$.
Hence, $\left[O{H}^{-}\right]={10}^{-11}$.