Question

$pH$ of a buffer solution decreases by $0.02$ units when $0.12\,g$ of acetic acid is added to $250\, mL$ of a buffer solution of acetic acid and potassium acetate at $27^{\circ} C$. The buffer capacity of the solution is

• A. 0.1
• B. 10
• C. 1
• D. 0.4

Answer 1

Answer: (D)

0.4

Answer 2

Buffer capacity, $\beta=\frac{d C_{ HA }}{d_{ pH }}$,
where, $d C_{ HA }=$ no. of moles of acid added per litre
$d_{ pH } =$ change in $pH$
$d C_{ HA } =\frac{\text { moles of acetic acid }}{\text { volume }}$
$=\frac{0.12 / 60}{250 / 1000}=\frac{1}{125}$
$\therefore \beta =\frac{1 / 125}{0.02}=\frac{1}{2.5}=0.4$