Chemistry : Buffers

Question

An aqueous solution contains 0.34 M potassium fluoride.

One liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.)

___ 0.33 mol KNO₃

___ 0.16 mol HClO₄

___ 0.16 mol Ca(OH)₂

___ 0.33 mol HF

___ 0.34 mol HClO₄

Answer 1

Since a buffer is composed of a weak acid (or weak base) and the conjugate base (or conjugate acid), and we have the conjugate base of hydrofluoric acid (KF), we need to have the weak acid, HF. The only choice is

0.33 mol HF

In summary, in this case, the buffer must contain the weak acid, HF, and the salt of that acid, KF.