Equal volumes of $0.5 \mathrm{N}$ acetic acid and $0.5 \mathrm{N}$ sodium acetate are mixed. What is the $\mathrm{pH}$ of resultant solution?

(${\mathrm{pK}}_{\mathrm{a}}$ of acetic acid $=4.75$)

The mixture of the acetic acid and sodium acetate acts as an acidic buffer. The pH of the solution can be calculated using Hendersen equation as shown below.

$\mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}+\log \frac{\left[\mathrm{sodium} \mathrm{acetate}\right]}{\left[\mathrm{acetic} \mathrm{acid}\right]}$

Given that $\left[\mathrm{Sodium} \mathrm{acetate}\right]=\left[\mathrm{acetic} \mathrm{acid}\right]$

Hence, $\mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}=4.75$