Question

Part A What is the pH of a 0.270 M ammonia solution? Express your answer numerically to two decimal places.

Part B What is the percent ionization of ammonia at this concentration? Express your answer with the appropriate units.

Answer 1

A) Kb of NH3 = 1.8 x 10^-5   so it is weak base.

for weak bases

pOH = 1/2 (pKb - log C)

pOH = 1/2(-log kb - log 0.27)

pOH = 1/2 (-log 1.8 x 10^-5 - log 0.27)

pOH = 1/2 (4.7+0.57)

pOH =2.64

PH = 14 - 2.64

pH = 11.36

B) Kb = c alpha² / (1 - alpha) (alpha = extent of dissociation)

1.8 x 10^-5  = 0.27 alpha / 1- alpha

(1.8 x 10^-5) - (1.8 x 10^-5 alpha) = 0.27alpha²

0.27 alpha²  + 0.000018 alpha - 0.000018 = 0

by solving qudratic equation alpha = 0.0081

% ionization = 0.0081 x 100 = 0.8