Question

What is the $O{H}^{-}$ concentration of an aqueous solution of a substance whose pH is 3.2?

• A. ${10}^{-3.8}$
• B. ${10}^{-3.2}$
• C. ${10}^{-10.8}$
• D. ${10}^{-10.2}$

Answer 1

The correct option is C ${10}^{-10.8}$

The pH of solution is negative logarithm of hydrogen ion concentration.

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

Hence, $\left[H^{+}\right]={10}^{-pH}={10}^{-3.2}$

$\left[H^{+}\right]\left[O{H}^{-}\right]={10}^{-14}$

$\left[O{H}^{-}\right]=\frac{{10}^{-14}}{\left[H^{+}\right]}=\frac{{10}^{-14}}{{10}^{-3.2}}=1\times {10}^{-10.8}$ M.

Option C is correct