which of these solutions is the most basic? i thought it was [OH-]=1*10^-13. BUT the answer is [H+]= 1*10^-11. HOW COME THAT IS THE ANSWER?

Answer 1

Let's review a little.
pH of solution with (H^+) = 1 x 10^-11 = 11.
A solution with (OH^-) = 1 x 10^-13 is pOH = 13; therefore, pH = 14 - 13 = 1. So pH 11 is MUCH more basic than pH of 1.

OR you can look at it another way.
If (OH^-) = 1 x 10^-13, then
(H^+)(OH^-) = Kw
(H^+) = Kw/(OH^-) = 1 x 10^-14/1 x 10^-13 = 1 x 10^-1 and compare that with (H^+) = 1 x 10^-11. The 1 x 10^-11 is much more basic since 10^-11 is a very small number and much less than 10^-1

Answer 2

ahaa, that makes sense, thanks for you help doc. ;)