Homework Help: Chemistry

Posted by Anonymous on Monday, July 16, 2012 at 3:36pm.

The absorbance of a chlorophyll a standard solution in ethanol (density = 0.785 g/mL) is measured in
a 1.3 cm cuvette or path length. The absorbance is 0.435 and the molar absorptivity coefficient is 86,300 M–1cm–1.
The molecular weight for chlorophyll a is 893.49 g/mol.

The absorbance of a chlorophyll a standard solution in ethanol (density = 0.785 g/mL) is measured in
a 1.3 cm cuvette or path length. The absorbance is 0.435 and the molar absorptivity coefficient is 86,300 M–1cm–1.
The molecular weight for chlorophyll a is 893.49 g/mol.

A) What is the molar concentration of the solution? (I've already gotten.)

B) What is the concentration of the solution in ppm?

Chemistry - DrBob222, Monday, July 16, 2012 at 4:03pm
What did you get for M? If I call that 4E-6M (an estimate on my part) then that is
4E-6 mols/L EtOH or 4E-6 mols/785g (since density is 0.785g/mL then 1000 mL will have a mass of 785 g).
4E-6 mols x molar mass = grams chlorophyll = about 0.004 g chlorophyll. That is in 785g soln or 0.004/785 = about 5E-6 g/g. That makes it 5E-6*(10^6/10^6) = about 5 ppm.
That makes chlorophyll 4E-6/785 =
Chemistry - Anonymous, Monday, July 16, 2012 at 4:07pm
The molar concentration is 3.87E-6.
Chemistry - Anonymous, Monday, July 16, 2012 at 4:12pm
thank you!
Chemistry - Anonymous, Monday, August 27, 2012 at 10:31pm
i still don't get it

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