ELECTIVES > AQUATIC CHEMISTRY

Five major topics will be explored: 1) acid-base chemistry, 2) dissolution/precipitation, 3) complexation, 4) oxidation and reduction, and 5) adsorption. Students will be exposed to methods used for calculating the chemical composition and speciation of solutions at thermodynamic equilibrium. The application of equilibrium models to actual environmental problems will be stressed, and at the end of the course students should be capable of reading and understanding the primary literature. There will be a heavy emphasis on problem solving using approximation and graphical methods as well as the computer program MINEQL+. An additional goal of this course is to help students learn the strengths and limitations of the equilibrium approach.

Required Text: Aquatic Chemistry Concepts by James F. Pankow, Lewis Publishers

Required Software: MINEQL+ 3.0 A chemical equilibrium program for personal computes. from: Environmental Research Software. Note: This program is available at no cost to students in accordance with the copyright.

Recommended Text: Aquatic Chemistry Problems, J.F. Pankow Titan Press - this is a series of worked out problem sets that go along with the readings.

Supplemental Readings: Additional papers from the primary literature will be handed out to supplement the textbook readings.

Class Structure and Grading:
Lecture and discussion 1.5 hours - Tuesday and Thursday
Computer lab office hours 1 afternoon per week
Problem Sets (nine; 0-5 points each) 45%
Weekly Quizzes (ten , 0-3 points each) 30%
Term Paper 25%

What to expect:

Each week students will be given a series of problems to solve some of these problems will be worked out using the computer program MINEQL+ but many will involve calculations using approximation and graphical methods and a hand calculator. Students are encouraged to work together on the problem sets. Problem sets will be handed in each Tuesday and discussed in class. Every Thursday there will be a short 10 minute quiz which covers the readings and discussion from the previous two lectures.

Each student will be asked to identify a problem of interest to them for a term paper. Examples of projects include, controls on iron sulfide mineral formation in recent sediments, nitrogen dynamics in soils, the role of the oceans in buffering the CO2 content of the atmosphere, modeling adsorption in soils for predicting the effects of acid rain on aquatic ecosystems, controls on pCO2 in soil water, controls on silica concentrations in the oceans, regulation of the oxygen content of the atmosphere. Students may also chose to incorporate a detailed chemical analysis of their research project for the core courses. Students will be expected to read research papers on their topic, and write a report on the current hypotheses, which include quantitative calculations and a discussion of the applicability of equilibrium models to the problem. I will help the student chose key reference papers and data sets for analysis. Term papers are due two weeks after the end of the lecture period.

Lectures:

 Lecture 1: Introduction to aquatic chemistry:

Topics covered: - Goals of the course, review of units and concentrations scales, ideal and non-ideal systems, activity and activity coefficients. What is chemical equilibrium analysis and how is it useful?, How do equilibrium models differ from kinetic models? What are the strengths and weaknesses of each approach? Examples of the application of equilibrium analysis to ecosystems biogeochemistry and environmental problems. Readings: Pankow Chapter 1

 

Lecture 2: Basic Thermodynamic Principles.

Topics covered: Free energy and chemical change, chemical potential, Using free energy change to understand reactions, free energy data sets - standard states and conventions, effects of temperature and pressure on equilibrium constants, combining equilibrium constants. Readings: Pankow Chapter 2.1 through 2.6

 

Lecture 3: More on concentrations scales and activity, The proton.

Topics covered: Ways to calculate activity - Davies, extended Debeye Huckel, and Guntleberg equations. The proton, what is the proton in solution? the importance of understanding what we measure when we measure pH. Readings: Pankow Chapter 2.7, 2.8, 3. Supplemental Readings (optional) - Measuring pH under different conditions

 

Lecture 4: Acid Base Chemistry I.

Topics covered: Solutions to equilibrium reactions using fundamental properties - proton balance, mass balance and electrical neutrality. General equations for predicting the behavior of a simple monoprotic acid (HA) and a simple base (NaA). Readings: Pankow Chapter 4, 5.1-5.3 inclusive.

 

Lecture 5: Acid-Base chemistry II.

Topics Covered: More acids and bases, including activity corrections, pH as a master variable, use of log concentration vs. pH plots. Readings: Pankow 5.4, 5.5, 6

 

Lecture 6: The dissolved CO2 system in natural waters, alkalinity, total carbon.

Topics covered: Gases in water - review of Henry’s law, definitions of alkalinity and total carbon, calculation of total carbon in systems open and closed to the atmosphere, inorganic carbon and the global C budget. Readings: Pankow 7, 9 (skip 9.83), hand out.

 

Lecture 7: Buffering, Alkalinity and Titrations.

Topics covered: How solution chemistry changes with the addition of strong acids or bases, equivalence points, practical methods - Gran titrations. Readings: Pankow 7, 10.1.10.2-10.24

 

Lecture 8: Precipitation and dissolution.

Topics covered: definition of saturation, undersaturation, supersaturation, calculating the solubility of simple salts, conventions used for solubility constants, metal oxides and hydroxides and carbonates. Reading: Pankow Chapter 11, 12.0-12.3 inclusive

 

Lecture 9: More on Mineral solubility.

Topics Covered: metal carbonates in systems open to the atmosphere - CaCO3 as an example, concentration vs. pH plots. Reading: Pankow Chapter 13.1-13.3, hand out.

 

Lecture 10: Mineral solubility and The Gibbs Phase rule.

Topics covered: solubility control, multiple solid phases, log concentration vs pH diagrams for multiple solid phases in closed systems, - iron minerals as an example, using the Gibbs Phase rule to constrain equilibrium calculations. Reading: Pankow Chapter 14, 17.1, 17.2 (look over examples in 17.7).

 

Lecture 11: Complexation.

Topics covered: Definitions of ligands and complexes , formation and dissociation constants of complexes, hydrolysis of metal ions, the importance of pH on hydrolysis, multiple ligands, the stepwise attachment of several ligands, chelates. Reading: Pankow Chapter 18 through 18.6.

 

Lecture 12: Oxidation Reduction - redox reactions, pe and Eh.

Topics covered: Half cell reactions, the concept of pe and pH, Eh and its relationship to pe, similarities and differences between pe and pH, similarity between redox and acid/base equilibria, the redox chemistry of water. Readings: Pankow 19.1 through 19.4. Supplemental Readings: Hand out on how to make Eh measurements

 

Lecture 13: Oxidation reduction continued - pe-pH diagrams.

Topics covered: Constructing pe-pH diagrams - a simple example where there are no solid phases hydrogen, oxygen and aqueous chlorine, including solids. Readings: Pankow Chapter 20, and 21

 

Lecture 14: Oxidation Reduction in natural waters I

Topics covered: Chemistry of C, and N in natural waters, controls on pe in natural systems, chemical vs. biological control. Readings: Pankow Chapter 23-23.3.2.5 inclusive

 

Lecture 15: Oxidation Reduction in natural waters II

Topics covered: Chemistry of S and Fe, in natural systems. Readings: Morse et al. 1987 "The chemistry of the hydrogen sulfide and iron sulfide systems in natural waters", Earth-Sci. Rev. 24:1-42 and Pankow Chapter 23.3.-23.4

 

Lecture 16: Oxidation - Reduction III

Topics covered: The evolution of oxygen in the atmosphere, a planetary scale redox titration. Readings: Holland "Atmospheric Oxygen and the biosphere" pp127-136 in Jones and Lawton (eds) Linking Species and Ecosystems, Chapman and Hall, NY. Supplemental Readings Pankow Chapter 24. Note: Holland is a possible guest lecturer

 

Lecture 17: Adsorption

Topics covered: Theory of the electrical double layer in aqueous systems, inner sphere surface complexes, the role of ligands in promoting or retarding dissolution. Readings: Pankow 26.1, 26.2, 26.3, Stumm 1995 "The inner sphere surface complex: A key to understanding surface reactivity".In: Huang et al. (eds) Aquatic Chemistry: Interfacial and Interspecies Processes.

 

Lecture 17: Ion Exchange

Topics covered: What is ion exchange, treating ion exchange as an equilibrium problem, electrostatic sorption in ion exchange. Readings: Dzombak and Hudson, 1995 Ion Exchange: The contributions of diffuse layer sorption and surface complexation" In: Huang et al. (eds) Aquatic Chemistry: Interfacial and Interspecies Processes.

 

Lecture 18: Practical approaches to modeling adsorption and ion exchange

Topics covered: Langmuir, Freundlich and linear models, what to do with messy systems, using empirical data to determine adsorption coefficients, examples of successful models using adsorption. Reading: Weber et al. 1995, " Distributed reactivity in the sorption of hydrophobic organic contaminates in natural aquatic systems" In Huang et al. (eds),

 

Lecture 19: More examples of equilibrium models and how equilibrium models can be combined with kinetic models.

Readings: Mattigod, S. 1995 Chemical Equilibrium and Reaction Models: Applications and future trends. pp1-5 In: Chemical Equilibrium and Reaction models, SSSA Special publication 42., Crosby et al. 1985, Modeling the effects of acid deposition: Assessment of a lumped parameter model of soil water and stream water chemistry Water Resources Research 21: 51-63.

 

Lecture 20: Review, discussion of projects

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