Question

The dissociation constant of acetic acid $K_a$ is $1.74\times {10}^{-5}$ at $298K$ . The $pH$ of a solution of $0.1M$ acetic acid is:

• A. 2.88
• B. 3.6
• C. 4.0
• D. 1.0
• E. 2.0

Answer 1

Answer: (A)

For $0.1M$ acetic acid, or $<br/>C=0.1J{K}^{-1}mo{l}^{-1}$
$K_a=1.74\times {10}^{-5}$
$pH=?$
According to Ostwald dilution formula,
$[H^{+}]=\sqrt{K_a\times C}$
$=\sqrt{1.7\times {10}^{-5}\times 0.1}$
$=\sqrt{0.017\times {10}^{-4}}$
$pH=-{\log }_{10}[H^{+}]$
$=-{\log }_{10}[\sqrt{0.017\times {10}^{-4}}]$
$pH=2.88$