Which of the following pairs constitutes a buffer?
Which of the following pairs constitutes a buffer?
$\mathrm{HCl}$ and $\mathrm{KCl}$
$\mathrm{HNO}_2$ and $\mathrm{NaNO}_2$
$\mathrm{NaOH}$ and $\mathrm{NaCl}$
$\mathrm{HNO}_3$ and $\mathrm{NH}_4 \mathrm{NO}_3$
Solution
The pair $\mathrm{HNO}_2$ and $\mathrm{NaNO}_2$ constitutes a buffer because $\mathrm{HNO}_2$ is a weak acid and $\mathrm{NaNO}_2$ is a salt of a weak acid $\left(\mathrm{HNO}_2\right)$ with a strong base $(\mathrm{NaOH})$. Hence, it is an example of an acidic buffer solution.
Caution
Solutions of a weak acid and its conjugate base or weak base and its conjugate acid are able to maintain $\mathrm{pH}$ forming buffer solutions.