Conduct a practical investigation to prepare a buffer and demonstrate its properties

Preparation of a buffer solution

Solutions whose pH remain unchanged even after addition of a small amount of acid or base is known as Buffer solution.
Preparation of acidic buffer and its properties:

Acidic buffers are generally produced by mixing a weak acid with its salt. For example mixture of CH₃COOH and CH₃COONa from the reaction,

Acidic buffers generally have a pH value of less than 7.
If the solution contained equal molar concentrations of both the acid and the salt, it would have a pH of 4.76.
When an acid is added to an acidic buffer, most of the H⁺ ion of the added acid is consumed by CH₃COO^–. CH₃COOH being a weak acid does not dissociate quickly thus, the pH is balanced.
When a base is added to this buffer, OH^–reacts with H⁺ obtained from the dissociation of CH₃COOH and forms neutral water. Until all the OH^– ions are removed, CH₃COOH keeps dissociating.

Preparation of basic buffer and its properties:
- Basic buffers are generally produced by mixing a weak base with its salt. For example mixture of NH₄OH and NH₄Cl from the reaction,

Acidic buffers generally have a pH value of greater than 7.
If the solution contained equal molar concentrations of both the acid and the salt, it would have a pH of 9.25.
On addition of an acid in this buffer, some of the H⁺ ion of the added acid is consumed by NH₃ while some react with OH^– to produce water. Thus, no significant pH change is observed.
When a base is added to this buffer, OH^–reacts with NH₄⁺ and most of the OH^– ions are eliminated in this way.