Q20 / 120 · VITEEE 2009 · Chemistry

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

  • A
    $0.1$
  • B
    10
  • C
    1
  • Correct answer
    D
    $0.4$

Solution

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

Hence, the correct answer is option: 'D'.

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