concentrations of an unknown using the calibration curves of pure dyes as you

did in the first UV-Vis lab.

You will need to determine the exact values of the ratios (3 and 31% in this

example) using your data, but the forms of the equations are identical, and you

just need to swap in whatever you find as the ratios in place of 0.03 and 0.31.

To determine masses of dyes in the drink mixes, you will also need to use the

molar masses of the dyes. The molar mass of FD&C Red No. 40 is 496.42 g/mol.

The molar mass of FD&C Yellow No. 5 is 534.39 g/mol. The molar mass of FD&C

Blue No. 1 is 792.85 g/mol.

Safety Considerations

Wear eye protection and wash hands regularly to avoid harmful materials having

contact with your eyes.

Disposal of Waste

All waste and excess reagents should be disposed of in the labeled waste

container in the room.

Pre-Lab Questions

1. Predict the wavelengths of maximum absorbance of red dyes, blue dyes, and

yellow dyes based on your knowledge of complementary colors.

2. If a 100.0 mL solution has a concentration of 1.0 x 10^-5 M of Blue Dye No.1,

how many milligrams of the dye are in the solution?

3. For a certain packet of Kool-Aid, the serving size is 8 grams of the drink mix.

In the question above, if you used 2 grams of drink mix to make the 100.0 mL

solution, how many milligrams of Blue Dye No. 1 would you consume in a

single serving?

4. Use the equations above, correcting for interference between Yellow No. 5 and

Red No. 40 dyes. You measure a drink mix that contains Yellow No. 5 and Red

No. 40. The absorbance at 425 nm is 0.65. The absorbance at 505 nm is 0.43.

What are the corrected absorbance values that you would use to determine

the individual dye concentrations when you use the calibration curves made

for the pure dyes?

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