Hydrogen cyanide, HCN (), is a pale blue, highly volatile liquid. Its solution in water is called hydrocyanic acid. HCN (aq) + H2O () H3O+ (aq) + CN- (aq) If the Ka is 6.2 x 10-10 in a 0.20 mol/L solution of HCN (aq), what is the concentration of the hydronium ion