posted by krystal .
As the pH of a system decreases:
the [H+] decreases
the Kw decreases
the [OH-] decreases
all of the above
As the pH decreases the H^+ gets larger.
Kw is a constant and changes only with temperature.
If pH gets smaller, H^+ becomes larger and OH becomes smaller.
Look at (H^+)(OH^-) = Kw.
If H goes up, OH must go down. If OH goes up, H^+ must go down. Kw doesn't move so H or OH must if the other one moves.
so the answer would be OH- decreases