Question

11. The Kw of water varies with temperature. Calculate the pH of water at 46⁰C with a Kw = 1.219 x 10-14. Show all calculations leading to an answer.

Answer 1

Remember that in water, the concentration of hydronium ions, or H⁺, will equal the concentration of hydroxide ions. That is [H⁺] = [OH⁻].

Remember that Kw = [H⁺][OH⁻] for water and if [H⁺] and [OH⁻] are both equal, we can easily solve for them by taking the square root of Kw.

[H⁺] = sqrt(1.219*10^-14) = 1.104*10^-7

and remember that pH = -log[H⁺] = -log(1.104*10^-7) = 6.9570

(The rules for sig figs are that if you take the log of a number with x significant figures, then the result should have x significant decimal places.)

The pH of water is 6.9570