Anyone good at calculating concentrations using pH?

Question

Can you calculate the concentration of a KOH aqueous Solution with a pH of 10.5?

Answer 1

pH of 10.5 means a pOH of 3.5. OH- concentration will then be 10^-3.5, or 3.16 x 10^-4.

Answer 2

Well, the pH is defined as -log(H+ concentration). So, to go backwards, use the 10^x function. 10^(-3.40) = 3.98e-4 M. To find the OH- concentration, first find the pOH using the pH. Since pH + pOH = 14, 14 - pH = pOH. 14 - 3.40 = 10.60 Now do the inverse log thing again to find the concentration of OH-. 10^(-10.60) = 2.51e-11 M To the correct amount of sig figs, the [H+] is 4.0e-4 M, the pOH is 10.60, and the [OH-] is 2.5e-11 M.