Find the PH solution of dimethylamine

Question

K_b of dimethylamine [(CH₃)₂NH] is 5.90^x10^–4 at 25°C. Calculate the pH of a 0.0140 M  solution of dimethylamine.

Answer 1

(CH₃)₂NH + H₂O ==> (CH₃)₂NH₂⁺ + OH^-

Kb = 5.90x10^-4 = [(CH₃)₂NH₂⁺] [OH^-] / [(CH₃)₂NH]

5.90x10^-4 = (x)(x) / 0.0140 - x

Use the quadratic formula to solve for x which will be the [OH-]

Take the negative log to get pOH

Subtract pOH from 14 to get pH