Question

pH of an aqueous solution containing $10^{-8}mol/L$ of $HCl$ is

• A. 8
• B. 10
• C. 6.96
• D. 12

Answer 1

Answer: (C)

If the concentration of acid is less than
$10^{-7}$, then the concentration of
$H^{+}$present in water is not neglected.
Total $\left[H^{+}\right]=\left[H^{+}\right]$
from $HCl+\left[H^{+}\right]H_{2}O$
$=10^{-8}+10^{-7}$
$=10^{-7}(1.1)$
$=1.1\times 10^{-7}mol/L$
$pH=-\log \left[H^{+}\right]$
$=-\log \left(1.1\times 10^{-7}\right)$
$=6.96$