Question

Which of the following is the correct equilibrium expression for an aqueous solution of the conjugate base of hydrocyanic acid, HCN:

1) K_a = [ H₃O⁺ ] [ CN^- ] / [ HCN ]

2) K_a = [ HCN ] [ OH^- ] / [ CN^- ]

3) K_b = [ HCN ] [ OH^- ] / [ CN^- ]

4) K_a = [ H⁺ ] [ CN^- ] [ HCN ]

5) K_b = [ H₃O⁺ ] [ CN^- ] / [ HCN ]

Answer 1