Question

What is the pH of a solution which is 0.600 M in dimethylamine ((CH3)2NH) and 0.400 M in dimethylamine hydrochloride ((CH3)2NH2Cl)? Kb for dimethylamine = 7.4x10-4.

Answer 1

Answer:

pH = 11.05

Explanation:

It is possible to answer this question using Henderson-Hasselbalch formula:

pH = pka + log₁₀ [A] / [HA⁺]

Where A in this case is weak base (dimethylamine) and conjugate acid (HA⁺) is dimethylamine hydrochloride.

As Ka= Kw / Kb = 1x10⁻¹⁴ / 7.4x10⁻⁴ = 1.35x10⁻¹¹ And pKa is -log Ka = 10.87 pH of the solution is:

pH = 10.87 + log₁₀ [0.600] / [0.400]

pH = 11.05

I hope it helps!