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