Question

$\mathrm{pKa}$ of Acetic acid is $4.74$. The concentration of ${\mathrm{CH}}_3\mathrm{COONa}$ is $0.01\mathrm{M}$. The $\mathrm{pH}$ of ${\mathrm{CH}}_3\mathrm{COONa}$ solution is?

Answer 1

Step 1: Balanced chemical equation

${\mathrm{CH}}_3\mathrm{COONa}$ is a salt of the weak acid ${\mathrm{CH}}_3\mathrm{COOH}$ and a strong base $\mathrm{NaOH}$.

$\underset{\mathrm{Sodium}\mathrm{Acetate}}{{\mathrm{CH}}_3\mathrm{COONa}\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}\left(\mathrm{l}\right)\leftrightharpoons \underset{\mathrm{Acetate}\mathrm{acid}}{{\mathrm{CH}}_3\mathrm{COOH}}\left(\mathrm{aq}\right)+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}$

This is the case of salt hydrolysis.

Step 2: Calculating $\mathrm{pH}$

The pH scale indicates how acidic or alkaline an aqueous solution is and normally it has a range of values from 0 to 14.

The pH value measures the concentration of Hydrogen ions or Hydroxide ions.

The lower the pH value, the higher the concentration of Hydrogen ions.

$$\begin{gathered} \mathrm{pH}=7+\frac{1}{2}\mathrm{pKa}+\frac{1}{2}\left(\mathrm{logC}\right) \\ \mathrm{pH}=7+\frac{1}{2}\times 4.74+\frac{1}{2}\left(\log \right(0.01\left)\right) \\ \mathrm{pH}=7+2.37-1 \\ \mathrm{pH}=9.37-1 \\ \mathrm{pH}=8.37 \end{gathered}$$

The $\mathrm{pH}$ of ${\mathrm{CH}}_3\mathrm{COONa}$ solution is 8.37.