Explanation: Kb for NH3 is listed in the table as Kb = 1.8 x 10-5 . Using the equation we can calculate Ka for the conjugate acid NH4+ : Ka = Kw / Kb = 1.0 x 10^-14 / 1.8 x 10^-5 = 5.6 x 10^-10 Answer: 5.6 x 10^-10 Topic: acid dissociation constant