Q9 / 160 · TS EAMCET 2023 (12 May Shift 1) · Chemistry

A 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 diluted to $100 \mathrm{~mL}$. If the $\mathrm{pK}_{\mathrm{a}}$ of acetic acid is 4.76 , then the $\mathrm{pH}$ of the solution is

  • Correct answer
    A
    $4.76$
  • B
    $3.76$
  • C
    $5.76$
  • D
    $9.24$

Solution

$\begin{aligned} & \text { } \mathrm{pH}=\mathrm{pK}_{\mathrm{a}}+\log \frac{[\text { salt }]}{[\text { Acid }]} \\ & {[\text { Acid }]=\left[\mathrm{CH}_3 \mathrm{COOH}\right]=\frac{10 \times 1}{100}=0.1 \mathrm{M}} \\ & {[\text { Salt }]=\left[\mathrm{CH}_3 \mathrm{COO}^{-}\right]=\frac{20 \times 0.5}{100}=0.1 \mathrm{M}} \\ & \Rightarrow \mathrm{pH}=4.76+\log \frac{0.1}{0.1} \\ & =4.76\end{aligned}$

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

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