Question

Why is dissociation of water important?

Answer 1

Well, it underlies our understanding of acid-base behaviour....

Explanation:

Water is just another solvent, admittedly it is a very important solvent, and one that provides the basis for ALL of biochemistry.

In the bulk solvent we conceive of acids, characteristic cations, and base, characteristic anions:

`H_2O(l) rightleftharpoonsH^+ + HO^-`

Alternatively.....

`2H_2O(l) rightleftharpoonsH_3O^+ + HO^-`

Just to note that in aqueous solution under standard conditions, the ion product...

`K_w=[H_3O^+][HO^-]=10^(-14)`...

And we can take `log_10` of both sides to give....

`log_(10)K_w=log_(10)10^(-14)=log_10[H_3O^+]+log_10[HO^-]`.

And thus.... `-14=log_(10)[H_3O^+]+log_(10)[HO^-]`

Or.....

`14=underbrace(-log_(10)[H_3O^+]-log_(10)[HO^-])_(pH+pOH=14)`

`14=pH+pOH`

This relationship allows us to make very accurate assessments of `pH` and acidity with relatively simple apparatus. Even with A level equipment, you can get exceptionally accurate and meaningful results in acid-base titrations.