Q10 / 160 · AP EAMCET 2019 (20 Apr Shift 2) · Chemistry

A buffer solution is prepared by mixing $10 \mathrm{~mL}$ of $1.0 \mathrm{M}$ acetic acid and $20 \mathrm{~mL}$ of $0.5 \mathrm{M}$ sodium acetate and then diluted to $100 \mathrm{~mL}$ with distilled water, The $\mathrm{pH}$ of the buffer solution is ( $\mathrm{p} K_a$ of acetic acid is 4.76 )

  • A
    4.84
  • B
    5.21
  • C
    4.34
  • Correct answer
    D
    4.76

Solution

Milliequivalents of acetic acid $=10 \mathrm{~mL} \times 1.0 \mathrm{M}$ Milliequivalents of sodium acetate $=2.0 \mathrm{~mL} \times 0.5 \mathrm{M}$ From Henderson equation, $$ \mathrm{pH}=\mathrm{p} K_a+\log \left[\frac{\text { salt }}{\text { acid }}\right] $$ Here, $\quad \mathrm{p} K_a=4.76$ [For acetic acid] $$ \begin{aligned} \because \quad \mathrm{pH} & =4.76+\log \left(\frac{0.5 \times 20}{10 \times 1.0}\right) \\ \mathrm{pH} & =4.76 \end{aligned} $$ Hence, option (d) is correct.

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

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