A solution of HCN (aq) is made. When the solution comes to equilibrium, which of the

following is true?

HCN (aq) = H + (aq) + CN - (aq) with Kc = 7.9 X 10-10

A. The reaction mixture will contain mostly HCN.

B. The reaction mixture will contain comparable amounts of HCN, H+, and CN".

C. The reaction mixture will contain mostly H + and CN ...

D. Cannot determine answer based on given information.

The reaction mixture will contain mostly HCN

Explanation:

For weak acids such as HCN with Ka = 7.69 x 10⁻¹⁰ at 25°C

Assume a molar concentration of 0.100M in deionized water ...

[H⁺} = [CN⁻] = √Ka·[Wk Acid] = √ (7.69 x 10⁻¹⁰) (0.10) = 8.76 x 10⁻⁶M ...

This is the maximum amount of ions delivered into solution from HCN in aqueous media at 25°C. Such represents a %ionization of only 8.77 x 10⁻³ % at 25°C. Yes, mostly HCN at equilibrium.