Question

Calculate the expected pH of solutions prepared as given below. a) 4mL 6 M acetic acid + 3.3 g sodium acetate trihydrate (MM= 136 g/mol) b) 4mL 6M acetic acid + 3.3 g sodium acetate trihydrate + 6mL 1M NaOH

Answer 1

a)

mmol of acid = MV = 4*6 = 24

mmol of acetate = mass/MW = 3.3/136 = 0.024264 = 0.024264*10{3 mmol = 24.264

pH = pKa + log(Acetate/Acid)

pH = 4.75 + log(24.264/24)

pH = 4.754

b)

mmol of acid = MV = 4*6 = 24

mmol of acetate = mass/MW = 3.3/136 = 0.024264 = 0.024264*10{3 mmol = 24.264

mmol of base = MV = 1*6 = 6

after reaction

mmol of acid left = 24-6 = 18

mmol of acetate formed = 24.264+6 = 30.26

pH = pKa + log(Acetate/Acid)

pH = 4.75 + log(30.26/18)

pH = 4.975