What is water on the pH scale?

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Answer 1 · 2016-10-16T19:13:16

Distilled water has $pH=7$ .

$pH$ , $"pouvoir hydrogene"$ , is a measure of hydrogen ion concentration in water (I think there is an accent in there somewhere but nevermind).

Aqueous acidity is conceived to be a measure of hydrogen ion concentration according to the following equilibrium:

$2H_2O rightleftharpoons H_3O^+ + H_3O^+$

And at $298K$ , $K_w=[H_3O^+][HO^-]$ $=$ $10^-14$ .

Taking $-log_10$ of both sides, we get the defining relationship:

$pH + pOH=-log_10(10^-14)=14$ .

At neutrality under standard conditions, thus $pH=pOH=7$ .