Question

If the hydrogen ion concentration in an acid is $10^{-8}mol/L$ then the $pH$

• A. 9
• B. 7
• C. < 7
• D. > 8

Answer 1

Answer: (C)

$pH=-\log \left[H^{+}\right]$
$H^{+}=10^{-8}mol/L$
So, in aqueous solution, in $H^{+}$ion concentration of acid,
$H^{+}$ion concentration of water is also added.
Hence, total $\left[H^{+}\right]$of acid
$=\left(10^{-8}+10^{-7}\right)mol/L$
$=10^{-8}(1+10)$
$=11\times 10^{-8}mol/L$
Therefore, $pH=-\log \left[11\times 10^{-8}\right]$
$=-\log 11+8\log 10$
$=-1.0414+8$
$pH=6.9586$