Acids and Bases: Buffer Action

Question 1

Define the term buffer

Answer 1

• A buffer is a solution that resists changes in pH when small amounts of acid or alkali are added

Question 2

What does an acidic buffer contain?

Answer 2

• Mixture of a weak acid with one of its salts

- Weak acid and salt must be in high concentration

Question 3

What does a basic buffer contain?

Answer 3

• Mixture of weak base with one of its salts

- Weak base and salt must be in high concentration

Question 4

How does an acid buffer resist the change in pH after addition of a base?

Answer 4

• E.g CH3COOH ⇌ CH3COO- + H+
• The OH- concentration increases
• Most of extra OH- ions react with H+ ions to form water - decreasing H+ concentration
• Equilibrium shifts to right to oppose decrease in H+ ions
• H+ concentration increases so pH doesn’t become alkaline

Question 5

How does an acidic buffer resist the change in pH after addition of an acid?

Answer 5

• E.g CH3COOH ⇌ CH3COO- + H+
• H+ concentration increases
• Equilibrium shifts to the left to oppose increase in H+ concentration
• Extra H+ ions react with salt ions (CH3COO-) to form weak acid (CH3COOH)
• H+ concentration decreases so pH doesn’t become acidic

Question 6

How does a basic buffer resist changes in pH after addition of a base?

Answer 6

• E.g NH3 + H+ ⇌ NH4+
• OH- ions react with H+ ions to form water
• Equilibrium shifts to left to oppose decrease in H+ concentration
• H+ concentration increases so pH doesn’t become alkaline

Question 7

How does a basic buffer resist changes in pH after addition of an acid?

Answer 7

• E.g NH3 + H+ ⇌ NH4+
• H+ concentration increases
• Equilibrium shifts to right to oppose increase in H+
• H+ reacts with NH3 to form NH4+
• H+ concentration decreases so pH doesn’t become acidic