Why is dissociation of water important?

1 Answer
Dec 31, 2017

Answer:

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.