Adjustment of Analyte Oxidation State

Sometimes we need to adjust the oxidation state of analyte before it can be titrated. For example, Mn2+ can be preoxidized to MnOj and then titrated with standard Fe2+. Preadjustment must be quantitative, and you must eliminate excess preadjustment reagent. 

Several powerful oxidants can be easily removed after preoxidation. Peroxydisulfate (S20, also called persulfate) is a strong oxidant that requires Ag+as a catalyst. 

Excess reagent is destroyed by boiling the solution after oxidation of analyte is complete. 2S20 - + 2H20- 4S0 - + Oz + 4H+ 

Silver(II) oxide (AgO) dissolves in concentrated mineral acids to give Ag2+, with oxidizing power similar to S2Ojj plus Ag+. Excess Ag2+ can be removed by boiling  

Solid sodium bismuthate (NaBi03) has an oxidizing strength similar to that of Ag2+ and S201. Excess solid oxidant is removed by filtration. 

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