Ch.7 - Activity and the Systematic Treatment of EquilibriumWorksheetSee all chapters
All Chapters
Ch.1 - Chemical Measurements
Ch.2 - Tools of the Trade
Ch.3 - Experimental Error
Ch.4 + 5 - Statistics, Quality Assurance and Calibration Methods
Ch.6 - Chemical Equilibrium
Ch.7 - Activity and the Systematic Treatment of Equilibrium
Ch.8 - Monoprotic Acid-Base Equilibria
Ch.9 - Polyprotic Acid-Base Equilibria
Ch.10 - Acid-Base Titrations
Ch.11 - EDTA Titrations
Ch.12 - Advanced Topics in Equilibrium
Ch.13 - Fundamentals of Electrochemistry
Ch.14 - Electrodes and Potentiometry
Ch.15 - Redox Titrations
Ch.16 - Electroanalytical Techniques
Ch.17 - Fundamentals of Spectrophotometry
BONUS: Chemical Kinetics
Sections
Ionic Strength of Soluble Salts
Activity Coefficients
pH Revisited

Activity coefficients is factor used in describing the departure from ideal behavior for a reaction mixture. 

Activity Coefficients

Concept #1: In order to express the effect of ionic strength on the concentration of species we calculate its activity with the use of an activity coefficient, which is given in units of gamma.

Example #1: For the following compound, state the solubility product expression with its activity coefficient. 

Cu2(SO4)3

Example #2: For the following compound, state the solubility product expression with its activity coefficient.

Mo2S5

Activity Coefficient Table

Example #3: Find the activity coefficient for the ion specified in the following compound:

Na+ in 0.005 M NaCl 

Example #4: Find the activity coefficient for the ion specified in the following compound:

CN  in 1.0 mM RbCN

Example #5: Find the activity coefficient for the ion specified in the following compound:

Zr4+ in 5.0 mM Zr(NO3)4

Practice: Calculate the activity coefficient of H+ using the extended Debye-Huckel equation for a solution comprised of H+ and I . Given that H+ has a size of 9.00 x 10-10 m and the molar concentration of the solution is 0.075.  

log γ = − 0.51 z 2 µ / 1 + (α µ / 305)

Interpolation: Non-ideal Ionic Strength

Concept #2: Sometimes the ionic strength of a dissolvable compound you calculate may not be found on your chart and other means will be require to find the activity coefficient. 

Example #6: Find the activity coefficient from the given ionic strength, µ, for the following ion.

Ba2+ when µ = 0.075

Practice: Find the activity coefficient from the given ionic strength, µ, for the following ion.

F   when µ = 0.0080