When a 0. 1 m aqueous solution of hydrocyanic acid, HCN, reaches equilibrium, the ka for hydrocyanic acid is 3.969 x 10⁻¹⁰.
It's the value of equilibrium constant for the dissociation of ions into a solution. The more the Ka value the more will be dissociation.
Ka = [H₃O⁺]² / [HCN] [H₃O⁺]
The pH is 5.20
-log [H₃O⁺] = 5.20
Putting antitlog both side.
The value will be 6.30 x 10⁻⁶
Ka = (6.30 x 10⁻⁶)² / 0.1 - 6.30 x 10⁻⁶
0.1 - 6.30 x 10⁻⁶ = 0.1
Ka = 3.969 x 10⁻¹⁰
Thus, the Ka value for hydrocyanic acid is 3.969 x 10⁻¹⁰.
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