Question about acid and base

1) What is the pH of a solution 0.10 M in ammonia and 0.151 M in ammonium chloride? (Kb for ammonia 1.80x10^-5)

pOH = pKb - log([NH3]/[NH4^+])
pOH = -log(1.8 x 10^-5) - log(0.1/0.151) = 4.92
pH = 14 - 4.92 = 9.08


2) What volume(in mL) of 0.33M HCl solution must be added to 222mL of 0.27M ammonia solution to give a buffer solution with pH8.5?(Kb for ammonia 1.80x10^-5)

Let V mL HCl is added.
H^+(aq) + NH3(aq) ≒ NH4^+(aq)
Origin no. of moles of NH3 = 0.27 x (222/1000) = 0.05994 mol
No. of moles of HCl added = 0.33 x (V/1000) = 0.00033V mol
At equilibrium, [NH3]/[NH4+] = (0.05994 - 0.00033V)/0.00033V

pOH = pKb - log([NH3/NH4^+])
14 - pH = -log(Kb) - log([NH3/NH4^+])
14 - 8.5 = -log(1.8 x 10^-5) - log[(0.05994 - 0.00033V)/0.00033V]
log[(0.05994 - 0.00033V)/0.00033V] = -0.755
(0.05994 - 0.00033V)/0.00033V = 10^(-0.755) = 0.176
0.05994 - 0.00033V = 0.000058
0.000388V = 0.05994
V = 154.5 mL


3) What is the pH of a solution 0.167M in acetic acid and 0.189M in soldium acetate? (Ka for acetic acid 1.75X10^-5)

pH = pKa - log([CH3COOH]/[CH3COO^-]
pH = -log(1.75 x 10^-5) - log(0.167/0.189) = 4.81