Department of Earth Science |Northeastern Illinois University

AQUEOUS GEOCHEMISTRY
ESCI 406
Spring, 2005
Homework #4: Due Wednesday, March 16, 2005                                                                     Sanders

Portfolio of Analyses

* The objective of this assignment is to determine whether a given water sample is in equilibrium with respect to a given geochemical reaction.  This will be based on the reactions you proposed in Homework #3. 

In Homework #3, you selected and wrote a reaction equation for five geochemical reactions, one for each of the five analysis sets included in your portfolio.  Now, you will examine each of those reactions, and selecting a single water analysis from that set, determine whether or not the water is in equilibrium with respect to that reaction. 

This homework assignment will form the second entry in your Portfolio of Analyses.  Please hand it in with the whole portfolio.  I will look at and potentially comment on the whole portfolio, but only this week's assignment will be graded.

The Assignment Give the balanced chemical equation for the reaction you chose for a given analysis set.  Give the value of the equilibrium constant (this should come from the results of Homework #3). Determine which dissolved species are involved in the geochemical reaction, and write the formula for the equilibrium constant involving activities of dissolved species. Select a water sample, and using the Debye-Hückel equation, determine the activity coefficient in that sample for each of the dissolved species involved in the reaction.   Calculate the Ion Activity Product (IAP) for the reaction for the water sample you chose. Using the Keq and the IAP, determine whether or not the water sample is in equilibrium with respect to the reaction.  If it is not, determine what direction the reaction would proceed (if it is reversible). Do this for each of the five analysis sets.  What to Put in the Portfolio * Create a cover page for this section; give it a meaningful title. * State the objective and explain basic terms and concepts that a reader would need to understand in order to understand your work (for example, IAP, equilibrium, reversible, and so on). * Describe your methods * Summarize your results in a neat table. * Discuss your results (e.g compare and contrast, put the results in their geologic context, etc.)

Things to Check Before Handing in the Portfolio

* Cite the source of every piece of information that is not taken from your own brain.  Use standard citation format!  (e.g. "Eby, 2005")
* Check your "References Cited" page, and make sure it includes all of the sources you have cited thus far, in proper format. 
* Make any corrections to previous versions of the portfolio (based on my comments on previous assignments, or your own edits/corrections.
* Hand in the whole portfolio with all the components listed here:
    - cover page
    - the current assignment, including its cover page
    - cover page for each analysis set
    - five analysis sets
    - References Cited
* Use dividers, tabs, or colored pages between sections.

© 2005 Laura L. Sanders.  Last updated March 9, 2005.