Question

What is the hydroxide ion concentration of a solution at 25∘C with a pH=9.90?

Round the answer to one decimal place.

Enter the answer in scientific notation.

Give answer in M

Answer 1

pH = 9.90

Now it is known that

pH + pOH = 14

or, pOH = 14 - pH

             = 14 - 9.90

             = 4.10

or, -log[OH^-] = 4.10         [ pOH = -log[OH^-]]

or, log[OH^-] = - 4.10

or, [OH^-] = 10^-4.10

                 = 7.9 x 10^-5 M

Therefore, hydroxide ion concentration of a solution at 25 ^oC = 7.9 x 10^-5 M