Remember that pH = -log[H⁺]
So [H⁺] = 10^(-pH)
also recall that Kw for water would be:
Kw = [H⁺][OH⁻]
Remember that in water, the concentration of hydronium ions, or H⁺, will equal the concentration of hydroxide ions. That is [H⁺] = [OH⁻].
[OH⁻] = [H⁺] = 10^(-7.53) = 2.9510^-8
(The rules for significant digits is when you take 10 to the power of something with x significant decimal places, then the result will have x significant digits. But for now keep some extra digits so we won't have rounding errors.)
Kw = (2.9510^-8)(2.9510^-8) = 8.7010^-16 = 8.710^-16
The Kw is 8.7*10^-16.
