Recitation Assignment 4

Due at the end of class

 Recitation Problem:

What is the temperature dependence of gypsum and anhydrite solubilities?

a)      Run example problem 2 from the PhreeqC example problem database

b)      Analyze output graph, what does it tell you about the relationship between these solubilities and temperatures (2 or 3 sentences is fine)?

c)   E-mail or turn in a copy of the graph along with your explanation.

Spreadsheet Assignment:

        a) By now you should have ionic strength (I) , activity coefficients (gamma), and activities based on the        

            Guntelberg approximation of the Debye-Huckle Equation. Now use these to calculate ion activity products   

            (Q),  for calcite and gypsum.

        b) Calculate the SI for calcite and gypsum (remember that SI = log(IAP/K) using these values.

        c) Then use PHREEQC to calculate SI values and compare with what you got with Guntelberg