Question

$1\times {10}^{-3}$ mole of $HCl$ is added to a buffer solution made up of $0.01M$ acetic acid and $0.10M$ sodium acetate. The final pH of the buffer will be: (given $p{K}_a$ of acetic acid is $4.75$ at ${25}^{o}C$)

• A. $4.60$
• B. $4.66$
• C. $4.75$
• D. $4.8$

Answer 1

The correct option is B $4.66$

${CH}_{3}CO{O}^{-}+H^{+}⟶{CH}_{3}COOH$
initially $0.01$ $0.001$ $0.01$
at equi. $(0.01-0.001)$ $0.01+0.001$
$=0.009$ $=0.011$

$pH=p{K}_a+\log \frac{salt}{acid}=4.75+\log \frac{0.009}{0.011}=4.66$