Question

a solution of OH- ions is added to a beaker of pure water at 25 C, to a final concentration of 872 nM. Calculate the pH of the solution. I know that pH=-log[H+], but I'm still really confused as to how to convert the nM to M and how to solve this problem.

Answer 1

I assume 872 nM is 872 nanomolar which would make it 872-9M or 8.72E-7M. The problem states that OH is ADDED UNTIL the OH^- is 8.72E-7M. Now, since (H^+)(OH^-) = 1E-14
Plug in OH and solve for H. I get 1.15E-8 M and convert that to pH.