Calculate the pH of the solution.

Question

A solution is prepared at 25 °C that is initially 0.33 M in methylamine (CH₃, NH₂), a weak base with K_b = 4,4 x 10^-4,

, and 0.074 M in methylammonium bromide (CH₃NH₃Br). Calculate the pH of the solution. Round your answer to 2 decimal places.

Answer 1

Methylamine is a weak base. methylamine bromide is the salt of that weak base. This solution creates a buffer and so we can use the Henderson Hasselbalch equation to find the pOH and then the pH:

pOH = pKb + log [salt] / [base]

pKb = -log Kb = -log 4.4x10^-4 = 3.36

pOH = 3.36 + log [0.074 M] / [0.33 M] = 3.36 + log 0.224

pOH = 3.36 - 0.65

pOH = 2.71

pH = 14 - 2.71

pH = 11.29