For an industrial wastewater that contains 1.0×10-4 M total CrVI at pH 8, a very common approach to remove Cr VI from water is to reduce Cr VI to Cr III, thereby forming the Cr(OH) 3 (s) precipitate that can be easily separated from water. The reduction can be accomplished by addition of ferrous sulfate (FeSO4 ) to the water. 1. If the amount of 1×10-4 M FeSO4 is added to reduce Cr VI, write out the balanced half reactions and the overall reaction for reduction of CrO42- by Fe 2+ to yield Cr(OH) 3 (s) and Fe(OH) 3 (s). 2. Demonstrate that the above reaction is thermodynamically favorable and will occur in this industrial wastewater.
Chromium is a priority metal pollutant and potential carcinogen that exists in two major
oxidation states (Cr III and Cr VI) in aquatic environments. In aqueous solution, Cr VI exists as the highly soluble oxyanions HCrO4- and CrO42-, and Cr III exists as Cr 3+
(aq) and hydroxo species.
Toxicologists believe that Cr VI oxyanions are the principle health concern. Changes in oxidation
state have a dramatic effect on chromium solid/solution partitioning and migration in soils and
aquifer sediments. Use the provided
diagram for Cr III as a function of pH, solve for the following questions.
For an industrial wastewater that contains 1.0×10-4 M total CrVI at pH 8, a very common
approach to remove Cr VI from water is to reduce Cr VI to Cr III, thereby forming the Cr(OH) 3 (s) precipitate that can be easily separated from water. The reduction can be accomplished by
addition of ferrous sulfate (FeSO4 ) to the water.
1. If the amount of 1×10-4 M FeSO4 is added to reduce Cr VI, write out the balanced half
reactions and the overall reaction for reduction of CrO42- by Fe 2+ to yield Cr(OH) 3 (s) and
Fe(OH) 3 (s).
2. Demonstrate that the above reaction is thermodynamically favorable and will occur in this industrial wastewater.
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