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118. Solving a chemistry problem
Content: 28.rar 22,3 kB
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28. The optical density of a solution containing 1.00 mg of caffeine C8H10O2N4 * H2O in 100.0 ml of 0.005 M H2SO4 is 0.510 at 272 nm in a cuvette with l = 1.00 cm. A sample of instant coffee weighing 2.5000 g was dissolved in water and diluted to 500 ml. An aliquot of the resulting solution (25.0 ml) was placed in a volumetric flask with a capacity of 500 ml, 25.0 ml of 0.1 M H2SO4 was added, clarified, and then the solution was diluted to the mark. The optical density of this solution, measured under the same conditions, was found to be 0.415. Calculate the mass of caffeine in 100.0 instant coffee. Mol. mass (C8H10O2N4*H2O) 212.1.
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