Hydrogen Ion Activity

by Ned

I want to add a slight clarification of hydrogen activity versus hydrogen concentration. Hydrogen activity can be thought of as applying a correction factor to the hydrogen concentration. Activity is related to concentration by the Hydrogen activity coefficient:

a(H) = K(a) x c(H)


a(H) = Hydrogen activity in the solution
K(a) = Hydrogen activity coefficient
c(H) = Hydrogen concentration in the solution

Hydrogen activity indicates how many hydrogen ions seem to be present in the solution and is different from how many actually are present (concentration).

Most pH measurements are in extremely dilute water solutions where the hydrogen ion concentration is the same as the hydrogen ion activity, K(a) is thus equal to 1.

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Apr 11, 2013
Hydrogen activity and Hydrogen concentration - have different nature
by: Lev

Hydrogen activity is relative difference between concentrations of ions H and OH in water. For example, electrolyzed water can have PH = 5 or PH = 8-10 at the same concentation of hydrogen ions H in water.

Oct 07, 2012
by: Leena

The hydrogen activity coefficient will change if the temperature of the solution change.

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