Kw for water?

Question

Given that Kw for water has a value of 51.3e-14 at 100C, the pH of pure water at 100C is...

5.626
6.145
7
7.213
8.316

I have no clue how to solve these kinds of questions. I thought Kw can only be 1e-14. Thanks to anyone.

Answer 1

The Kw is cited for a given temperature. As temp. goes up, more ions can exist, so the Kw goes up. To find the pH, Take the square root of Kw, which about 7.1 x10-7. Then pH= 7-log 7.1 or 6.145.