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