gg425h2a - GG425 - ENVIRONMENTAL GEOCHEMISTRY Homework set...

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GG425 -- ENVIRONMENTAL GEOCHEMISTRY Homework set #2 (partial answers) Here are answers to a few of the homework problems (the ones most people found to be more difficult). Please let me know if any of this is unclear of if you would like assistance with one of the other problems. Problem 2 From Fig. 4.4, we see that Fe in pure water of pH=9.5 and pE = -8.0 that Fe is as Fe(OH) 2 . Fe is in the +2 oxidation state. What happens when we add CO 2 to the solution? Is Fe(OH) 2 still the dominant form of Fe? There is a figure in the lecture notes showing the Fe + CO 2 + S system that indicates that at some conditions siderite (FeCO 3 ) or pyrite (FeS 2 ) are more favored (the "dominant phase"). We have no sulfur, so we needn't worry about pyrite. Siderite could form, however, in the problem 2 scenario. Notice that Fe is in the +2 oxidation state in this compound as well. So, the question is not a redox problem, it is a solubility one. With CO 2 present in solution at low pE and basic pH, which material is less soluble, Fe(OH)
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This note was uploaded on 04/12/2008 for the course CHEM 161 taught by Professor Yoshimoto during the Fall '05 term at Hawaii.

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gg425h2a - GG425 - ENVIRONMENTAL GEOCHEMISTRY Homework set...

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