Buffers

Buffer

A solution that resists changes in pH when small amounts of acid or base are added, or it’s diluted.

Acidic buffers

Buffers that have a pH lower than 7 and consist of a mixture of a weak acid and one of its salts.

Basic buffers

Buffers that have a pH higher than 7 and consist of a mixture of a weak base and one of its salts

How is an acidic buffer made

By mixing a solution with a high [HA] with a solution with a high [A^-]

What occurs when a small amount of acid is added to an acidic buffer

Equilibrium shifts to the left and [A^-] is high and reacts with the added H⁺ ions so [H⁺] hardly changes

What occurs when a small amount of base is added to an acidic buffer

OH^- will react with H⁺ shifting equilibrium to the right. There is a high [HA] and so some can dissociate so [H⁺] hardly changes

Everyday applications of buffers

• Shampoos have a slightly acidic buffer for shiny hair

• Blood needs to be kept at a constant pH just above 7 so enzymes don’t denature

• Buffers are used in food product as pH changes cause by bacteria or fungi can cause food to deteriorate

How to calculate pH of acidic buffer solutions

• Use the K_a expression

• For buffers [H⁺] ≠ [A^-]

• [H⁺] = K_a[HA] / [A^-]

Techniques and procedures for measuring the pH of a solution

• Use a pH probe

• After using the pH probe in one solution, rinse it with distilled water before testing another as some acid/base could remain on the pH probe