Q37 / 180 · KCET 2011 · Chemistry

A buffer solution contains $0.1$ mole of sodium acetate dissolved in $1000 \mathrm{~cm}^{3}$ of $0.1 \mathrm{M}$ acetic acid. To the above buffer solution, $0.1$ mole of sodium acetate is further added and dissolved. The $\mathrm{pH}$ of the resulting buffer is

  • A
    $\mathrm{p} K_{a}$
  • B
    $\mathrm{p} K_{a}+2$
  • C
    $\mathrm{p} K_{a}-\log 2$
  • Correct answer
    D
    $\mathrm{p} K_{a}+\log 2$

Solution

$\mathrm{pH}=\mathrm{p} K_{a}+\log \frac{\text { [salt] }}{\text { [acid] }}$ When extra $0.1$ mole sodium acetate is added [salt $]=0.2 \mathrm{~mol} \mathrm{dm^{-3 }}$ [acid] $=0.1 \mathrm{~mol} \mathrm{dm}^{-3}$ $\therefore \quad \mathrm{pH}=\mathrm{p} K_{a}+\log \frac{[0.2]}{[0.1]}$ $\mathrm{pH}=\mathrm{p} K_{\mathrm{a}}+\log 2$

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

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