Question

A buffer solution contains 0.11 mol of acetic acid and 0.14 mol of sodium acetate in 1.00 L.

Part A

What is the pH of this buffer?

Express your answer using two significant figures.

pH =

4.8

Part B

What is the pH of the buffer after the addition of 2×10⁻² mol of KOH?

Express your answer using two significant figures.

pH =

Part C

What is the pH of the buffer after the addition of 2×10⁻² mol of HNO3?

Express your answer using two significant figures.

pH =

Answer 1

Part B

no of moles of base = 2 x 10^-2 mol

on addition of ’ C’ moles of base to acidic buffer salt moles increases and acid moles decreases

so

pH = pKa + log [Salt +C/acid - C]

      = 4.74 + log [0.14 + 0.02 / 0.11 - 0.02]

      = 4.99

pH = 4.99

PART C

no of moles of acid = 2 x 10^-2 mol

on addition of ’ C’ moles of acid to acidic buffer salt moles decreases and acid moles increases

so

pH = pKa + log [Salt –C/acid + C]

      = 4.74 + log [0.14 - 0.02 / 0.11 + 0.02]

      = 4.70

pH = 4.7