CHEM 531 and CHEM 431 - Chemistry of Aquatic Systems

HYD 507 - Hydrogeochemistry

Dr. Michael Pullin

New Mexico Tech, Fall 2009

Tuesdays and Thursdays, 12:30-1:45 PM, Jones Annex 104

 

Course syllabus (updated 09/16/09)

 

Homework

Homework #1

Homework #2

Homework #3

 Homework #4

  1. From the Morel and Hering book chapter, do problem 2.5. In your result, include a Tableaux, mole balances, your analysis of each line equation, and the final graph. Use graph paper and draw the graphs by hand.
  2. Using the NIST Database, look up the equilibrium constants for the cadmium hydroxide, chloride, and sulfate complexes at ionic strength = 0 and 25 degrees Celcius. Keep in mind that the search engine is case sensitive. Chloride can be found as "Chloride," sulfate can be found as "Sulfuric acid," and hydroxide can be found as "Hydroxide."
    1. Write out the chemical reactions that are represented by each equilibrium constant.
    2. The hydroxide complexes are defined using hydroxide as a component. Convert each constant to using a proton (H+) as a component and calculate the new equilibrium constant for that reaction.
    3. Write a Tableau and mole balances for this system using Cd2+, Cl-, SO42-, H+, and H2O as components. Include the log K values in the Tableaux. Assume that the solution has the recipe of: Cd(NO3)2 = 1e-6 M, HCl = 1e-4 M, and Na2SO4 = 1e-3 M.

Homework #5

  1. Using Titrator do Example 3.2 from your textbook. However, don't negect the formation of the Cd-OH complexes. Instead of using the equilibrium constants provided in the book, use the values you determined for Homework #4.
    1. Solve the system using the pH conditions provided in the book. Since [HCl] = 1.0 M, that means pH = 0. Save and e-mail your titrator file to Dr. Pullin (mpullin@nmt.edu).
    2. Change the H+ component from a total molarity component to a free molarity component. Set the log free H+ = -8.1 (pH = 8.1, which is seawater pH). Solve the system again. Save and e-mail your titrator file to Dr. Pullin (mpullin@nmt.edu).
    3. Using the results from parts a and b, explain how the systems at pH = 0 and pH 8.1 are different.
  2. Using Titrator and starting with your solution to problem 1, sweep the chloride concentration from 1e-4 M to 10 M at pH = 0 and pH = 8.2. Export the data to a spreadsheet and plot the concentrations of all of the Cd-containing compounds and species as a function of the log free chloride concentration at both pH values (a separate graph for each pH). Save and e-mail your speadsheet file to Dr. Pullin (mpullin@nmt.edu).
  3. Do problem 4 at the end of Chapter 3 in your book. Use the NIST database as your source of equilibrium constants. Ignore the formation of PbSO4 (s, anglesite). Note that both chloride and H+ will be free components. You will vary chloride as specified in the problem. Log H+ will be fixed at -8.1. Sulfate will be a total component with a total concentation of 0.028 M. Pb will be a total component with a total concentration of 1e-6M. Export the data to a spreadsheet and plot the concentrations of all of the Pb-containing compounds and species as a function of the log free chloride concentration. Save and e-mail your speadsheet file to Dr. Pullin (mpullin@nmt.edu).

Homework #6

  1. The log Ksp for calcite (CaCO3) is -8.48 at 25 degrees celcius and ionic strongth = 0. Calculate the value of this Ksp at ionic strength = 0.1 M using the three commonly used approaches, the full Debye-Huckel equation (see Tables 4.1 and 4.2 in your book for parameters), the Debye-Huckel limiting law, and the Davies equation. Show your work.
  2. The log Ksp for gypsum (CaSO4 x 2H2O) is -3.78 at 25 degrees celcius and ionic strongth = 0.1. Calculate the value of this Ksp at ionic strength = 0 and ionic strength = 0.05 M using the full Debye-Huckel equation (see Tables 4.1 and 4.2 in your book for parameters). Show your work.

Homework #7

  1. Do Problem 1 at the end of Chapter 5 in the Langmuir textbook. Solve this problem by hand and turn in your work. Ignore the effects of ionic strength.
  2. Do Problem 2 at the end of Chapter 5 in the Langmuir textbook. You may solve this problem by hand or use Titrator. If you solve it by hand, turn in your work. If you solve it using titrator, turn in your set up for the problem (e.g. reactions, species, components, Tableau, mole balances). Ignore the effects of ionic strength.
  3. Do Problem 4 at the end of Chapter 5 in the Langmuir textbook. Use Titrator to solve this problem. In addition to the plot described in the problem, turn in a table of the concentrations of the various species as a function of pH (an e-mailed spreadsheet is fine) and your Tableau with log K values. Assume the system is closed. Use the equilibrium constants given in lecture 19 for the carbonate species and the equilibrium constant given in the book for acetic acid and assume they are all valid for an ionic strength of 0. As part of the solution, account for a fixed ionic stength = 0.01 M.
  4. Use Titrator to make a plot of the carbonate species versus pH (as in problem 2 of this assignment). However, change the system to one that is open to Earth's atmosphere. In addition to the plot described in the problem, turn in a table of the concentrations of the various species as a function of pH (an e-mailed spreadsheet is fine) and your Tableau with log K values. Assume PCO2 = 10^-3.5 atm. Use the same ionic strength as in problem 2. Don't include acetic acid in this problem.

Homework #8

  1. Do Problem 2 at the end of Chapter 6 in the Langmuir textbook. Use Titrator to solve this problem. Show the chemical reactions you considered, their equilibrium constants, and the Tableau and mole balance equations you used. The best way to solve this problem is to use solid CaCO3 as a total component and make the total concentration fairly high so that the resulting solution at equilibrium is saturated (i.e. add enough so that all of the CaCO3 does not dissolve).
  2. Calculate plot the speciation of iron(III) as a function of pH, including the possibility of solid formation. Assume the total iron concentation is 10^-6 M. Note that four possible iron(III)-hydroxide solids are listed in the NIST database. Consider the formation of the most soluble solid (i.e. the one with the largest Ksp value, log K = -38.6 at I=0 and 25 degrees; this solid is amorphous ferric hydroxide). In addition to plotting each of the species' concentration as a function of pH, also plot the total dissolved iron(III) concentration (i.e. the sum of the aqueous iron(III) species) as a function of pH.
  3. Calculate and plot the speciation of iron(II) as a function of pH, including the possibility of solid formation. Assume the total iron concentation is 10^-6 M and that the solution has a total carbonate concentration of 10^-3 M (closed system). Note that two possible iron(II)-hydroxide solids are listed in the NIST database. Consider the formation of the more soluble amorphous form. Also, don't forget to consider the formation of solid FeCO3. In addition to plotting each of the species' concentration as a function of pH, also plot the total dissolved iron(II) concentration (i.e. the sum of the aqueous iron(II) species) as a function of pH.

 

Lecture notes:

8/25/09

8/27/09

9/1/09

9/3/09

9/8/09

9/10/09

9/15/09

9/17/09

9/22/09

9/24/09

9/29/09

10/1/09

10/6/09

10/8/09

10/20/09

10/22/09

10/27/09

10/29/09

11/3/09

11/5/09

11/10/09

11/17/09

11/19/09

11/24/09

12/1/09

12/10/09

 

Titrator:

Download (zipped) - To "install" it, just copy the zip file to a "C:/titrator/" directory on the C: drive, and then unzip it. You can run the program by just double clicking on the titrator.exe file.

Instruction Manual

Tutorial