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 $HCl +\left[ H ^{+}\right] H _{2} O$
$=10^{-8}+10^{-7}$
$=10^{-7}(1.1)$
$=1.1 \times 10^{-7} mol / L$
$p H=-\log \left[ H ^{+}\right]$
$= -\log \left(1.1 \times 10^{-7}\right)$
$=6.96$