Calculate [\rm H_3O^+] given [\rm OH^-] in each of the following aqueous solutions.
[\rm OH^-] = 7.1×10^11M
What calculations do I make from this point? I have plugged in the 7.1×10^11M into the calculator but am getting the answer wrong every time and do not understand why. What other steps do I need to take to get the right answer?
I think you're looking at the problem wrong. Surely OH^- is not 7.1E11M. It may be 7.1E-11M.
(H^+)(OH^-) = Kw = 1E-14
(H^+)(7.1E-11) = 1E-14
(H^+) = 1E-14/7.1E-11 = 1.408E-4 which I would round to 1.4E-4 to two significant figures.