Chromium concentrations are generally below detection in anaerobic ground waters that contain ferrous iron. This may reflect reduction of soluble chromate (CrOr2-) to insoluble chromic ion (Cr(III)) by Fe2+ in a coupled redox reaction that can be written

CrO4-2- + 3 Fe2 + 8 H20 Cr(OH)3 + 3Fe(OH)3 + 4H+ 

The trace Cr(OH)3 is co precipitated with usually more abundant ferric oxyhydroxides. The equilibrium constant expression is 

Keq = 1012.8 = [H+]4/[CrO42-][Fe2+]3 

Ignoring activity coefficients, assume that pH = 7.0 and [Fe2+] = 10-6 M. What is the equilibrium concentration of chromate?

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Given Fe 10619 pH 70 also PH lognt ht 1... View the full answer