Question

which one of the following is a buffer solution? a) 0.40 M HCN and 0.10 KCN b) 0.20 CH3COOH c) 1.0 M HNO3 and 1.0 NaNO3 d) 0.10 M KCN e) 0.50 M HCl and 0.10 NaCl

Answer 1

Concepts and reason

The concept used to solve this question is based on buffer solutions.

A Buffer solution is an aqueous solution of weak acid and it’s conjugated or vice versa. A buffer solution shows little change in pH when a small quantity of acid or an alkali is added to it.

Fundamentals

Buffer are of two types acidic (buffer with pH<7) and basic (buffer with pH>7). The acidic buffer is made up by the combination of weak acid and conjugated base and on the other hand a basic buffer consists the combination of weak base and its conjugated acid.

A combination of weak acid and weak base cannot act as a buffer. A solution of weak base cannot act as a buffer. A solution of weak acid cannot act as a buffer.

Moreover, a strong acid and base pair can also not act as buffer as it would react and form a neutral salt.

Solution of weak acid HCN and its salt KCN can act as buffer. ${\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}$ dimers in the solution so it cannot act as a buffer. ${\rm{HN}}{{\rm{O}}_{\rm{3}}}$ and ${\rm{NaN}}{{\rm{O}}_{\rm{3}}}$ will form a neutral salt. KCN is a weak base. HCl and NaCl are strong acid-base pair they will form a neutral salt.

Ans:

A solution of 0.40 M HCN and 0.10 M KCN will act as a buffer.