Which one of the following is a buffer solution? 0.10 M KCN 0.20 M CH3COOH 1.0 M HNO3 and 1.0 M NaNO3 0.40 M HCN and 0.10 KCN 0.50 M HCl and 0.10 NaCl

0.40 M HCN and 0.10 KCN

Explanation:

A buffer solution is defined as the aqueous mixture of a weak base and its conjugate base or vice versa.

For the systems:

0.10 M KCN 0.20 M CH3COOH: Acetic acid, CH₃COOH is a weak acid and KCN is the conjugate base of HCN. Here, you have a weak acid and a conjugate base but not the conjugate base of the acetic acid or the weak acid of KCN. Thus, it is not a buffer.

1.0 M HNO3 and 1.0 M NaNO3. HNO₃ is a strong acid. Thus, this system is not a buffer.

0.40 M HCN and 0.10 KCN. Here, you have HCN, the weak acid, and KCN, its conjugate base. Thus, it is a buffer.

0.50 M HCl and 0.10 NaCl. HCl is a strong acid, thus, its mixture with NaCl is not a buffer.