Acid base and pH

Question

What is the hydroxide concentration [OH−] in an aqueous solution in which the hydronium

ion concentration [H3O^+] is 1×10^−5 M?

Answer 1

The hydronium ion concentration [H₃O^-] determines the pH. At [H₃O^-] = 1*10^-5 M, the pH = 5.

You can determine the hydroxide ion concentration by the pOH, which is defined as pOH = 14 - pH.

Therefore, pOH = 14 - 5 = 9; and the [OH^-] = 1*10^-9 M.