Tutorial 3 — Buffer Solutions

Learning Outcomes

Understand buffer solutions and their components
Calculate buffer pH using Henderson-Hasselbalch equation
Determine buffer capacity
Prepare buffer solutions of desired pH

Part A: Buffer Concepts

Question 1

a) Define a buffer solution. Explain how it resists changes in pH when small amounts of acid or base are added.

Extracted note: Buffer solution is a solution that maintains its pH when a small amount of acid or a base is added to it.

b) Identify the components needed to prepare:

An acidic buffer
A basic buffer

c) Why is a mixture of HCl and NaCl not a buffer solution?

Question 2

a) When a weak base is added to a solution that contains its conjugate acid, what type of buffer solution is produced?

Extracted answer: Because a weak base is added to a solution that contains its conjugate acid produce acidic buffer solution as product.

b) Calculate the pH of a buffer solution containing 0.10 M CH₃COOH and 0.15 M CH₃COONa. The $K_a$ of acetic acid is $1.8 \times 10^{-5}$.

Part B: Henderson-Hasselbalch Equation

Question 3

a) Derive the Henderson-Hasselbalch equation from the acid dissociation expression.

b) A buffer solution is prepared by mixing 50.0 mL of 0.20 M NH₃ with 50.0 mL of 0.10 M NH₄Cl. Calculate:

The pH of the buffer ($K_b$ for NH₃ = $1.8 \times 10^{-5}$)
The pH after adding 5.0 mL of 0.10 M HCl
The pH after adding 5.0 mL of 0.10 M NaOH

Question 4

a) What is the ratio of $[CH_3COO^-]/[CH_3COOH]$ required to prepare a buffer with pH 5.00?

b) How would you prepare 500 mL of this buffer starting with 0.20 M acetic acid and solid sodium acetate?

Part C: Buffer Capacity

Question 5

a) Define buffer capacity. What factors affect buffer capacity?

b) Which of the following buffer systems would have the greatest buffer capacity?

0.10 M CH₃COOH / 0.10 M CH₃COONa
1.0 M CH₃COOH / 1.0 M CH₃COONa
0.50 M CH₃COOH / 0.50 M CH₃COONa

c) Calculate the buffer capacity of a solution containing 0.20 M NH₃ and 0.20 M NH₄Cl when titrated with strong acid.

Part D: Biological Buffers

Question 6

a) Why is the carbonic acid-bicarbonate buffer system important in blood?

b) The pH of blood is maintained at 7.4. If the concentration of H₂CO₃ in blood is $2.4 \times 10^{-3}$ M and the $pK_{a1}$ of carbonic acid is 6.1, calculate the concentration of bicarbonate ion.

c) Explain what happens to blood pH during hyperventilation and how the buffer system responds.

Key Concepts

Buffer Solution — Solution that resists pH change upon addition of acid/base
Henderson-Hasselbalch Equation — $pH = pK_a + \log\frac{[A^-]}{[HA]}$
Buffer Capacity — Amount of acid/base a buffer can neutralize before significant pH change
Conjugate Acid-Base Pair — Pair of species related by proton transfer
pH — Measure of acidity

FAD1018 Tutorial 3 — Buffer Solutions