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.

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Question:

What is the H+ concentration for an aqueous solution with pOH = 3.47 at 25 C?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

pOH = -log([OH-]) ; by definition

[OH-] = concnetration of OH in mol per liter of solution

then

[OH-] = 10^-pOH = 10^-3.47 = 0.00033884415

note that, at 25°C

Kw = 10^-14 ALWAYS

then

Kw = [H+][OH-]

therefore

10^-14 = [H+] / (0.00033884415)

[h+] = (10^-14)/0.00033884415 =2.9512*10^-11

[H+] = 2.9512*10^-11

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