Redox in Soils

TABLE 5,7. Range of Eh Measurements of Soil-Water Systems 

Redox reactions in soils are affected by a number of parameters, including temperature, pH (see Chapter 7), and microbes. Microbes catalyze many redox reactions in soils and use a variety of compounds as electron acceptors or electron donors. For example, aerobic heterotrophic soil bacteria may metabolize readily available organic carbon using NO3, NOj, N20, Mn-oxides, Fe-oxides and compounds such as arsenate (As04 ) and selenate (Se04 ) as electron acceptors. Similarly, microbes may use reduced compounds or ions as electron donors, for example, NH4, Mn2+, Fe2+, arsenite (AsCXj), and selenite (SeO ). 

Explain the role of frontier electron orbital configuration on environmental chemistry. 

Explain, using equations, how redox chemistry affects mineral solubility. 

Consider all the parameters given in problem 3, with the only difference that activities are not equal concentrations (as expected). Calculate the concentrations of Fe3+ and Fe2+ assuming yFe = 0.3 and yFez+ = 0.6 at Eh of (a) 0.77 V, (b) 0.40 V, (c) 0.10 V, (d) 1.00 V, and (e) 1.20 V [hint see Chapter 2 about the use ofyj (i = any ion) in equilibria-type equations]. What can you conclude about the role of ion activity in redox systems  

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Bartlett, R. J. and B. R. James. 1992. Sunlight powered redox in soils and waters. Agronomy Abstracts, American Society of Agronomy, p. 233. Madison, WI. 

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