Question

A 280.0 mL buffer solution is 0.240 M in acetic acid and 0.240 M in sodium acetate.

Part A

What is the initial pH of this solution?

Part B

What is the pH after addition of 0.0150 mol of HCl?

Part C

What is the pH after addition of 0.0150 mol of NaOH?

Answer 1

the buffer equation:

mmol of acid = MV = 280*0.24

mmol of base = MV = 0.24*280

pH = pKa + log(A-/HA) = 4.75 + log(0.24/0.24) = 4.75

b)

mmol of HA = MV = 280*0.24 = 67.2

mmol of A- = MV = 67.2

after adding:

mmol of H+ = 0.015*1000 = 15

HA after = 67.2+15 = 82.2

A- after = 67.2-15 = 52.2

pH = pKa + log(A-/HA) = 4.75 + log(52.2/82.2) = 4.5527

c)

for OH-

after adding:

mmol of OH- = 0.015*1000 = 15

HA after = 67.2-15 = 52.2

A- after = 67.2+15 = 82.2

pH = pKa + log(A-/HA) = 4.75 + log(82.2/52.2) = 4.947201