As you dilute a solution, what happens to the #"pH"#?

#a)# It increases.
#b)# It decreases.
#c)# It stays the same.

1 Answer
Truong-Son N.
Dec 7, 2017

Assuming you don't add so much water that you drown out the #"H"^(+)# in solution... none of the above.

All solutions containing #"H"^(+)# or #"OH"^(-)# have a #"pH"# that changes with dilution... The more you add water, the smaller #["H"^(+)]# or #["OH"^(-)]# initially becomes (provided it is a relatively concentrated solution compared to #10^(-7) "M"# at #25^@ "C"#).

The mol fraction of water would tend towards #100%#.

Thus, the #"pH"# should tend towards neutral pH for whatever temperature this is at, whichever direction this needs to go (up for acidic solutions, down for basic solutions).

At the limit of infinite dilution, the #"pH"# stops changing and levels off at pH neutral.

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