What would be the $\mathrm{pH}$ of a solution obtained by mixing $5 \mathrm{~g}$ of acetic acid and $7.5…

What would be the $\mathrm{pH}$ of a solution obtained by mixing $5 \mathrm{~g}$ of acetic acid and $7.5 \mathrm{~g}$ of sodium acetate and making the volume equal to $500 \mathrm{~mL}$ ? $\left(\mathrm{K}_{\mathrm{a}}=1.75 \times 10^{-5}, \mathrm{pK}_{\mathrm{a}}=4.76\right)$
  1. $\mathrm{pH}=4.70$
  2. $\mathrm{pH} < 4.70$
  3. $\mathrm{pH}$ of solution will be equal to $\mathrm{pH}$ of acetic acid
  4. $4.76 < \mathrm{pH} < 5.0$

Solution

$\begin{aligned} \mathrm{pH} & =\mathrm{pK}_a+\log \frac{[\text { salt }]}{[\text { acid }]} \\ & =4.76+\log \frac{\frac{7.5}{500}}{\frac{5}{500}}=4.7+\log 1.5=4.87 \end{aligned}$ Hence correct answer is $4.76 < \mathrm{pH} < 5.0$

Asked in: JEE Main 2013 (25 Apr Online)

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