pH of a NaOH solution

Question

The pH of a NaOH solution is 13.29. What will be the pH of the solution when diluted to one million times?

Answer 1

pOH = 14 - pH = 14 - 13.29 = 0.71

[OH^-] = 0.195 M

Diluted 1 million times = 0.195 M / 106 = 1.95x10^-7 M

Adding in the 1x10^-7 M OH^- from autoionization of H₂O we would have...

1.95x10^-7 + 1.0x10^-7 = 2.95x10^-7 M OH^-

pOH = -log 2.95x10^-7 = 6.53

pH = 14 - pOH

pH = 7.47