Summary of Reactions of the members of the conjugate pair, HA/A-, in water

Summary of Reactions of the members of the conjugate pair, HA/A-, in water

•Acid Dissociation:

HA(aq) + H₂O <===> H₃O⁺(aq) + A^-(aq) K_eq = K_a(HA) = [H₃O⁺][A^-]/[HA]

•Reverse of Acid Dissociation:

A^-(aq) + H₃O⁺(aq) ® HA(aq) + H₂O K_eq = 1/K_a(HA) <===> [HA]/[H₃O⁺][A^-]

•Base hydrolysis:

A^-(aq) + H₂O <===> HA(aq) + OH^-(aq) K_eq = K_b(A^-) = K_w/K_a(HA) = [HA][OH^-]/[A^-]

•Reverse of Base Hydrolysis:

HA(aq) + OH^-(aq) ® H₂O + A^-(aq) K_eq = 1/K_b(A^-) = [A^-]/[HA][OH^-]

K_w is the equilibrium constant for autoionization of water: 2H₂O <===> H₃O⁺(aq) + OH^-(aq)

Example: HF/F-

HF(aq) + H₂O <===> H₃O⁺(aq) + F^-(aq) K_eq = K_a(HF) = [H₃O⁺][A^-]/[HF] = 6. 5 x 10^-4

F^-(aq) + H₃O⁺(aq) ® HF(aq) + H₂O K_eq = 1/K_a(HF) = [HF]/[H₃O⁺][F^-] = 1.5 x 10³

F^-(aq) + H₂O <===> HF(aq) + OH^-(aq) K_eq = K_b(F^-) = K_w/K_a(HF) = [HF][OH^-]/[F^-]

= 1.5 x 10^-11

HF(aq) + OH^-(aq) ® H₂O + F^-(aq) K_eq = 1/K_b(F^-) = [F^-]/[HF][OH^-] = 6.5 x 10¹⁰