What is the pH of 3.0M aqueous solution of NH3?

Question

NH3 information 

 

Base: NH3

 

Conjugate Acid: HF

 

Kb: 1.8×10^-5

 

pKb: 4.74

Answer 1

NH₃ + H₂O <==> NH₄⁺ + OH^-

Kb = [NH4⁺][OH^-]/[NH₃]

1.8x10^-5 = (x)(x)/3.0

x² = 5.4x10^-5

x = 7.35x10^-3 = [OH^-]

pOH = -log [OH^-] = -log 7.35x10^-3

pOH = 2.13

pH = 14 - pOH

pH = 11.87