Question

The next 3 questions will walk you through using the Henderson-Hasselbalch equation for the following question. For each step provide a numerical answer. A solution is made by combining 300mL of 0.020M trimethyl amine, that is (CH3)3N and a 500mL of a 0.03M solution of it's conjugate acid, that is (CH3)3NH . The Kb for trimethyl amine is 6.3x10-5. The Henderson-Hasselbalch equation uses pKa not Kb, Calculate the pKa....

Answer 1

Answer:

The pKa is 13.0.

Explanation:

pKa + pKb = 14

Given, Kb of trimethylamine = 6.3 × $10^{-5}$

pKb = - log (6.3 × $10^{-5}$)

= 1.0

⇒ pKa = 14 - pKb = 14 - 1.0

pKa = 13.0

Check: For most weak acids,  pKa ranges from 2 to 13.