Answer to Question #188401 in General Chemistry for Afa

Question

What is the pH of a 2.4x10^-4 M NH₃ solution? (K_b = 1.8x10^-5 )

Answer 1

NH3 reacts with water to form NH4OH

NH4OH is a weak base.

NH4OH(aq) = NH4+(aq) + OH-(aq)

Kb = [NH4+]×[OH-]/[NH4OH]

or,Kb= [OH-]^2/[NH4OH]

or,1.8×10^-5 = [OH-]^2/2.4×10^-4

or,[OH-]^2= 4.32×10^-9

or,[OH-] = 6.57×10^-5

pOH = -log[OH-]

= -log(6.57×10^-5)

= 4.18

Therefore, pH= 14–4.18

= 9.82

Hence the P^H of NH₃ solution is 9.82