Question

Explain why (Simple explanation)

Ionic strength increase then activity coefficient decrease

Ionic charge increase then activity coefficient increase

Ionic size increase then activity coefficient decrease

Answer 1

In solutions that are not too concentrated, the activity coefficient for a given species is dependent only on the ionic strength. As the ionic strength increases, an ion loses some of its effectiveness and its activity coefficient decreases.

In 1923 Peter Debye and Erich Hückel
developed an expression that allows one to calculate activity coefficients. The extended
Debeye-Hückel equation indicates that γ depends on three factors.

where z is the charge on the ion;
α is the hydrated ion radius (in pm);
μ is the ionic strength of the solution.

The ionic strength of a solution is a measure of electrolyte concentration and is
calculated by:

where c is the molarity of a particular ion and z is the charge on the ion. This is the
reason why KN depends on the electrolyte concentration.
A close look at the Debeye-Hückel equation shows that γ decreases as the ion
charge increases, the hydrated ionic radius decreases and as the ionic strength of the
solution increases. The effect of ionic strength on the activity coefficient strongly
depends on the charge of the ion