Question

The concentration of the $O{H}^{-}$ ions present in a solution having the pH value 2 at 298 K is ______.

• A. $1\times {10}^{2}M$
• B. $10\times {10}^{4}M$
• C. $1\times {10}^{-12}M$
• D. $1\times {10}^{12}M$

Answer 1

Answer: (C)

$1\times {10}^{-12}M$

The pH of solution is negative logarithm of hydrogen ion concentration.
$pH=-log\left[H^{+}\right]$
Hence, $\left[H^{+}\right]={10}^{-pH}={10}^{-2}$
$\left[H^{+}\right]\left[O{H}^{-}\right]={10}^{-14}$
$\left[O{H}^{-}\right]=\frac{{10}^{-14}}{\left[H^{+}\right]}=\frac{{10}^{-14}}{{10}^{-2}}=1\times {10}^{-12}$ M.