Chemistry: Ka Weak Acid Calculations

Question

The hydroxide ion concentration of an aqueous solution of 0.337 M hydrocyanic acid is ________ 

Answer 1

HCN ==> H⁺ + CN^-

Ka HCN = 6.2x10^-10

6.2x10^-10 = [H⁺][CN^-] / [HCN]

6.2x10^-10 = (x)² / 0.337

x² = 2.09x10^-10

x = 1.45x10^-5 = [H⁺]

[OH^-] = 1x10^-14 / 1.45x10^-5

[OH^-] = 6.9x10^-10 M