What is a Buffer Solution?

In this JC2 webinar let's discuss what a buffer solution is and the difference between an acidic and alkaline buffer.

A buffer is defined as a solution that maintains pH when small amounts of H+ or OH- is added.

This definition tells us the function of the buffer, but it does not tell us what makes up the buffer.

Personally I prefer to understand a buffer in this way:

Since a buffer can maintain pH when H+ is added, a base must be present to remove the added H+.

Similarly, since it can maintain pH when OH- is added, an acid must be present to remove the added OH-.

Hence a buffer is nothing more than a mixture of acid and base.

buffer solution diagram

The acid and base must be related to each other in order to coexist in the same system, ie a conjugate acid-base pair.

buffer solution mixture of conjugate acid base pair

Typically we will learn there are 2 types of buffers:

- acidic buffer is a mixture of weak acid and salt of conjugate base, eg CH3COOH + CH3COONa
- alkaline buffer is a mixture of weak base and salt of conjugate acid, eg NH3 + NH4Cl

Are these 2 buffer solutions really different?

Acidic Buffer

An acidic buffer is made up of a mixture of conjugate acid-base pair:

Acid is CH3COOH that will remove OH-
Base is CH3COO- that will remove H+

buffer solution acidic buffer

Alkaline Buffer

An alkaline buffer is also made up of a mixture of conjugate acid-base pair:

Acid is NH4+ that will remove OH-
Base is NH3 that will remove H+

buffer solution alkaline buffer

Fundamentally there is no real difference between an acidic and alkaline buffer.

The only difference is the buffering range:

- Acidic buffer maintains pH in the acidic region, ie pH less than 7
- Alkaline buffer maintains pH in the alkaline region, ie pH greater than 7

Topic: Buffer Solution, Physical Chemistry, A Level Chemistry, Singapore

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