The following information is to be used for the next two questions. Molar absorp

Question

The following information is to be used for the next two questions. Molar absorptivity data for the cobalt and nickel complexes with 2,3-quinoxalinedithiol are Co = 36400 and Ni = 5520 at 510 nm and Co = 1240 and Ni = 17500 at 656 nm. A 0.514-g sample was dissolved and diluted to 100.0 mL. A 25.0-mL aliquot was treated to eliminate interferences; after addition of 2,3-quinoxalinedithiol, the volume was adjusted to 50.0 mL. This solution had an absorbance of 1.246 at 510 nm and 0.367 at 656 nm in a 1.00-cm cell.
Calculate the concentration of cobalt (in ppm) in the initial solution prepared by dissolving the sample.

Explanation / Answer

(1.246+0.367)/2=0.8065

M=g/pf.*V

M=0.414541/(0.1*0.25)*58.9

M=0.2815 mol/L

0.2815 mol/L*58.9g/mol=16.58g/L=16600.581257117 ppm

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