1.
Activity and Activity Coefficient
• In a solution, diferent charged ions (cations and
anions) have electrostatic interaction. This
interaction in the neutral solutions do not have
between inons.
• When ions in a solution have high
concentrations, cations tend to be surrounded by
nearby anions and anions tend to be surrounded
by nearby cations. This effect is significant at ion
concentrations of 0.01 M and greater.

2.
Activity and Activity Coefficient
• When ions in a solution have high concentrations, cations tend to be
surrounded by nearby anions and anions tend to be surrounded by
nearby cations. This effect is significant at ion concentrations of 0.01
M and greater.

3.
Activity and Activity Coefficient
where Zi denotes the charge on an ion.
Ci is related to the formal concentration of each
ion.
The charge concentration of a solution is describe
by the ionic strength, which is calculated from the
following expression:

4.
Activity and Activity Coefficient

5.
Activity and Activity Coefficient
Based on these activity coefficients, the
equilibrium constants of ideal solutions can be
used to determine equilibria in non-ideal
solutions. Activity coefficients are unitless
numbers that are computed from the Debye-
Hückel equation:

6.
• Activity coefficients can be computed from the
Debye-Hückel equation:
Activity and Activity Coefficient

7.
Effective hydrated diameters of ions in aqueous solution (25 oC).
Cations Anions
Rb+, Cs+, NH4
+, Tl+, Ag+ 0.25
K+ Cl-, Br-, I-, NO3
-, HCOO- 0.3
OH-, F-, HS-, ClO4
-, MnO4
- 0.35
Na+ HCO3
-, H2PO4
-, HSO3
-, CH3COO- 0.4-0.45
Hg2
2+ HPO4
2-, SO4
2-, CrO4
2- 0.40
Pb2+ CO3
2-, SO3
2- 0.45
Sr2+, Ba2+, Cd2+, Hg2+ S2- 0.5
Li+, Ca2+, Cu2+, Zn2+
Sn2+, Mn2+, Fe2+, Ni2+, Co2+
Phthalate2-, C6H5COO- 0.6
Mg2+, Be2+ 0.8
H+, Al3+, Cr3+, Fe3+, La3+ 0.9
Activity and Activity Coefficient