Spectrophotometric determination of osmium
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m-Amino benzoic acid in large excess reacts with tetra-, hexa- and octavalent osmium at theph range 4.5–6 to give a purple complex having absorption maximum at 500 nm. Beer's law is obeyed for 0.5 to 8 ppm of osmium(VI) and osmium(VIII) with optimum concentration range of 2 to 8 ppm of osmium(VI) and 3 to 8 ppm for osmium(VIII). The per cent relative error per 1% absolute photometric error is 2.8 for both osmium(VI) and osmium(VIII). Ions such as Pd2+, Rh3+, Ir4+, W6+, U6+, Co2+, Hg2+, Mg2+, Ca2+, Ba2+, Sr2+, Th4+ and Zr4+ do not interfere in the determination.
Molar ratio method indicates that the reagent first reduces osmium (VIII) and osmium(VI) to osmium(IV), which then probably forms a 1∶1 complex with the excess unoxidised reagent.
KeywordsPhysical Chemistry Analytical Chemistry Inorganic Chemistry Hexa Relative Error
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