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

HF

Step-by-step 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.