Question

What substance would you add to KF(aq) to form a buffer solution? View Available Hint(s) What substance would you add to to form a buffer solution? HClO NaF NH3 KOH HF KCl

Answer 1

Answer

HF

Explanation

A buffer solution contains a weak acid and its conjugate base. The two species shall have a similar concentration in the solution. It's also possible for a weak base and its conjugate acid to form a buffer solution.

The KF solution already contains large number of $\text{F}^{-}$ ions. The objective is to thus find its conjugate acid or base.

$\text{F}^{-}$ contains no proton $\text{H}^{+}$ and is unlikely to be a conjugate acid. Assuming that $\text{F}^{-}$ is a conjugate base. Adding one proton to $\text{F}^{-}$ would produce its conjugate acid.

$\text{H}^{+} \; (aq) + \text{F}^{-} \; (aq) \rightleftharpoons \text{HF}\; (aq)$

Therefore $\text{HF}$ is the conjugate acid of $\text{F}^{-}$. $\text{HF}$ happens to be a weak acid. As a result, combining $\text{F}^{-}$ with $\text{HF}$ would produce a solution with large number of both the weak acid and its conjugate base, which is a buffer solution by definition.