A buffer solution of pH = 9.35 can be prepared by dissolving ammonia and ammonium chloride in water.?

Question

How many moles of ammonium chloride must be added to 1.0 L of 0.50 M ammonia to prepare the buffer?

a. 0.40 mol
b. 0.80 mol
c. 1.2 mol
d. 2.5 mol
e. 4.5 mol

Answer 1

a. 0.40 mol

[H+] at pH 9.35 is 4.47 x 10^-10
Ka for NH4+ is 5.70 x 10^-10
use this eqn to calculate [NH4+]

[NH4+] = ([H+] [NH3])/Ka