U2-1-6 - Buffers

Question 1

Buffer solution

Answer 1

A solution in which the pH remains approximately constant when small volumes of acid, base or water are added.

Question 2

An acid buffer consists of …

Answer 2

a weak acid and one of its salts (made from a strong base).

Question 3

A basic buffer consists of …

Answer 3

a weak base and one of its salts.

Question 4

Adding a small volume of water does not change buffer pH.

Why?

Answer 4

The acid and salt will be diluted by equal amounts.

(acid/salt ratio is unchanged)

Question 5

Sodium hydroxide is added to an acid buffer.

How does it resist change in pH?

Answer 5

H⁺ + OH^– → H₂O (removes H+ from solution)

acid equilibrium shifts to the right (HA ⇌ H⁺ + A^–)

Question 6

Sodium hydroxide is added to a basic buffer.

How does it resist change in pH?

Answer 6

H⁺ + OH^– → H₂O (removes OH^–)

Conjugate acid NH₄⁺ supplies H⁺ ions to replace ones removed

Question 7

Hydrochloric acid is added to a basic buffer.

How does it resist change in pH?

Answer 7

H⁺ + OH^– → H₂O (weak base removes H⁺)

Base equilibrium shifts to the right to replace OH^–

Question 8

Hydrochloric acid is added to an acid buffer.

How does it resist change in pH?

Answer 8

Conjugate base (from the salt) absorbs H⁺ to form weak acid