How to determine Acidic and Alkaline Buffer Solutions - Ionic Equilibria

In this video we want to discuss Buffer Solutions.

Definiton of a Buffer Solution

We know that a buffer solution is one that maintains pH when small amounts of H+ or OH- is added to it.

This means that inside this buffer, the following components must be present:

- an acid to remove OH-

- a base to remove H+

This mixture of acid and base must be of a conjugate acid-base pair, otherwise the acid and base will neutralise each other in the same solution.

buffer solution mixture of conjugate acid base pair

Acidic Buffer

An acidic buffer is a mixture of weak acid and salt of conjugate base.

An example is a mixture of CH3COOH and CH3COONa.

For this mixture of conjugate acid-base pair:

- CH3COOH is the acid that removes OH-

- CH3COO- is the base that removes H+

buffer solution acidic buffer example

We can show how H+ and OH- is removed via neutralisation reactions:

buffer solution acidic buffer reactions

Since H+ and OH- is removed, therefore pH is maintained.

Alkaline Buffer

An alkaline buffer is a mixture of weak base and salt of conjugate acid.

An example is a mixture of NH3 and NH4Cl.

For this mixture of conjugate acid-base pair:

- NH4+ is the acid that removes OH-

- NH3 is the base that removes H+

buffer solution alkaline buffer example

We can show how H+ and OH- is removed via neutralisation reactions:

buffer solution alkaline buffer reactions

Since H+ and OH- is removed, therefore pH is maintained.

For the detailed step-by-step discussion on how an acidic and alkaline buffer work, check out this video!

Topic: Ionic Equilibria, Physical Chemistry, A Level Chemistry, Singapore

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