Homework #4: Due Wednesday, October 23, 2002                                                     Sanders

This assignment will form one of the entries in your portfolio of analyses, the semester-long project that will be due December 9.  (See the entry in the syllabus for more information.)

Using the sets of water analyses that you collected earlier this semester, choose four water sample analyses.  These may be all from separate analysis sets, or they may be all from the same set; the option is yours.

For each of the samples, make the assumption that the water is in equilibrium with respect to the carbonate equilibria (except for the dissolution of calcite equilibrium).  Using the reported concentration of bicarbonate, as well as the pH and temperature, calculate the following:

    * activity of carbonate in the sample
    * activity coefficient for carbonate in the sample
    * calculated molality of carbonate in the sample

Show--and explain in words--your methods.  Explain, compare, and contrast the results of your analyses.

An alternative assignment:  If you have samples that include analyses of carbonate, go through the above steps, and then compare the calculated carbonate concentration with the measured carbonate concentration.  If you choose this option, you may limit your work to three analyses instead of four.

What if your analysis doesn't include bicarbonate, but instead gives alkalinity?  If you have an analysis that gives "alkalinity" instead of bicarbonate or HCO3-, then you'll need to convert the alkalinity values to bicarbonate values.  Check the units in which the alkalinity is reported, and then see me or consult the Hem book or the Drever textbook for hints on making the conversion.  If you choose this option, you may limit your work to three analyses instead of four.

© 2002 Laura L. Sanders.  Last updated October 16, 2002.