Answer to Question #343222 in Inorganic Chemistry for Sophie

Question

Calculate the concentration of OH^- in a 0.15 M solution of NH₃. K_b = 1.8 × 10^-5

Answer 1

NH₃ + H₂O = NH₄⁺ + OH^-

1) Kb = [NH₄⁺] * [OH^-] / [NH₃] .where, [NH₄⁺] and [OH^-] are equal, so we denote them by X

K_b = X * X / [NH₃] or

K_b = X² / [NH₃]

2) 1,8 * 10^-5 = X² / 0,15

X=√(1,8*10^-5 * 0,15) =√2,7*10^-6 = 1,64 *10^-3

ANSWER: [ OH^- ] = 1,64 *10^-3 M