Question

A steel sample weighing 1.000 g is dissolved in acids and treated with persulfate and periodate to oxidize Mn to MnO₄^- and Cr to Cr₂O₇^-. The solution is finally diluted to 100.00 mL in a volumetric flask. An aliquot placed in a 1.00-cm cuvette yielded an absorbance of 0.113 at 440 nm and of 1.304 at 545 nm. The absorbance for a reagent blank was 0.005 at 440 nm and 0.008 at 545 nm. Calculate the percentages (m/m) of Cr and Mn in the steel. The molar absorptivity of Cr₂O₇^- is 369 M^-1cm^-1 at 440 nm and 11 M^-1cm^-1 at 545 nm whereas that of MnO₄^- is 95 M^-1cm^-1 at 440 nm and 2350 M^-1cm^-1 at 545 nm. The molar mass of Mn is 54.94 g/mol and that of Cr is 52.00 g/mol.

Answer 1