21 Buffers

Question 1

What is a buffer

Answer 1

A system that minimises pH changes when small amounts of an acid or an alkali are added.

Question 2

What are the two components of a buffer solution in equilibrium?

Answer 2

A weak acid (HA)
Its conjugate base (A-)

Question 3

What happens when an acid is added to a buffer system?

Answer 3

• H+ ions are added
• Initially the concentration of H+ increases
• The large reservoir of A- ions react with the excess H+ ions
• The equilibrium position moves to the left
• H+ concentration and pH are restored

Question 4

What happens when an alkali is added to a buffer system?

Answer 4

• OH- ions are added
• OH- ions react with the H+ ions
• The concentration of H+ decreases
• The reservoir of HA molecules dissociate
• The equilibrium position moves to the right.
• The H+ concentration and pH are restored.

Question 5

What are the two approaches to preparing a buffer solution?

Answer 5

1. Mix a solution containing the weak acid with a solution that contains a salt of the weak acid.
2. Add an aqueous solution of an alkali to an excess of a weak acid

Question 6

What is the equivalence point?

Answer 6

The volume of one solution that exactly reacts with the volume of the other solution.