Water ionizes by the equation H2O(l)H+(aq)+OH(aq) The extent of the reaction is

Question

Water ionizes by the equation H2O(l)H+(aq)+OH(aq) The extent of the reaction is small in pure water and dilute aqueous solutions. This reaction creates the following relationship between [H+] and [OH]: Kw=[H+][OH] Keep in mind that, like all equilibrium constants, the value of Kw changes with temperature.

Part A: At a certain temperature, the pH of a neutral solution is 7.24. What is the value of Kw at that temperature? Express your answer numerically using two significant figures.

Part B: What is the pH of a neutral solution at a temperature where Kw=9.9×1014? Express your answer numerically using two decimal places.

Explanation / Answer

A)

pH = 7.24

[H+] = 10^-pH = 5.75 x 10^-8 M

[H+] = [OH-]= 5.75 x 10^-8 M

Kw = [H+] [OH-]

Kw = (5.75 x 10^-8)^2

Kw = 3.3 x 10^-15

part B)

Kw = [H+]^2

9.9 x 10^-14 = [H+]^2

[H+] = 3.15 x 10^-7 M

pH = -log[H+]

pH = 6.50

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