141. Solving a chemistry problem

141. Solving a chemistry problem

The optical density of a solution containing 1.00 mg of caffeine C8H10O2N4 ∙ H2O in 100.0 ml 0.0050 mol / L H2SO4 is 0.510 at 272 nm in a cuvette with a thickness of 1.0 cm. A sample of soluble coffee weighing 2.5000 g was dissolved in water and diluted to 500.0 ml. An aliquot of the resulting solution of 25.0 ml was placed in a volumetric flask with a capacity of 500.0 ml, 250 ml of 0.100 mol / L H2SO4 was added, clarified, and then the solution was diluted to the mark. The optical density of this solution, measured under the same conditions, turned out to be equal to 0.415. Calculate the mass of caffeine in pounds (453.6 g) of instant coffee. Molar mass М (С8Н10О2N4 ∙ H2O) = 212.1 g / mol.

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