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#.