Question

The dissociation constant of an acid $HA$ is $1\times {10}^{-5}$ the $pH$ of $0.1$ molar solution is:

• A. 5
• B. 4
• C. 3
• D. 2

Answer 1

Answer: (A)

5

$HA\rightleftharpoons H^{+}+A^{-}$

$\left[H^{+}\right]=0.1M;[H^{+}{]}^2=K_a\times C$

$\left[H^{+}\right]=\sqrt{K_a\times C}=\sqrt{1\times {10}^{-5}\times 0.1}=\sqrt{{10}^{-6}}$

$\left[H^{+}\right]={10}^{-3}M;pH=3$