Q2 / 60 · KVPY 2011 (SA) · Chemistry

An aqueous buffer is prepared by adding $100 \mathrm{ml}$ of $0.1 \mathrm{~mol} \mathrm{t}^{-1}$ acetic acid to $50 \mathrm{ml}$ of $0.2 \mathrm{~mol} \mathrm{I}^{-1}$ of sodium acetate. If $\mathrm{pKa}$ of acetic acid is $4.76$, the $\mathrm{pH}$ of the buffer is

  • A
    $4.26$
  • B
    $5.76$
  • C
    $3.76$
  • Correct answer
    D
    $4.76$

Solution

Meq of $\mathrm{CH}_{3} \mathrm{COOH}=100 \times 0.1 \times 1=10$ Meq of $\mathrm{CH}_{3} \mathrm{COONa}=50 \times 0.2 \times 1=10$ $\begin{array}{l} \mathrm{pH}=\mathrm{pK}_{\mathrm{a}}+\log \frac{\left[\mathrm{CH}_{3} \mathrm{COO}^{-}\right]}{\left[\mathrm{CH}_{3} \mathrm{COOH}\right]} \\ \mathrm{pH}=4.76+\log \frac{10}{10} \\ \mathrm{pH}=4.76+\log 1 \\ \mathrm{pH}=4.76 \end{array}$

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

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