"An aqueous solution contains 0.34 M hydrocyanic acid. 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.)"

0.34mol NaCN

0.082mol Ba(OH)₂

Explanation:

Options:

0.34mol NaCN

0.33mol NaClO₄

0.34mol HClO₄

0.16mol HClO₄

0.082mol Ba(OH)₂

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

Hydrocyanic acid, HCN is a weak acid. Its equilibrium in water is:

HCN + H₂O → CN⁻ + H₃O⁺

Where the CN⁻ ion is the conjugate base.

Thus, to convert the HCN solution in a buffer you must add CN⁻ ions to the solution.

In solution, 0.34mol NaCN converts 0.34 mol CN⁻, thus, you can convert this solution in a buffer with this addition.

The addition of HClO₄ or NaClO₄ don't produce a buffer because you would not have CN⁻ ions in solution.

Now, HCN reacts with Ba(OH)₂ thus:

2HCN + Ba(OH)₂ → 2H₂O + Ba²⁺ + 2CN⁻

Thus, the addition of 0.082mol Ba(OH)₂ could convert this solution in a buffer because CN⁻ is produced in its reaction with HCN