uv spectroscopy lab

Question

Obtain solutions of the following dyes in water at the given weights per liter: Quinoline yellow (13 mg), Methylene blue (2.5 mg), Phenolphthalein indicator solution (pink when pH>9). As part of your pre-lab, you must complete your calculations and note them in your notebook.

Answer 1

That's the type of information you should have included in your original post. You should go in the lab and follow those instructions.

The reason you measure against water is so you can use water as a blank or a control. Any absorbance from pure water will be subtracted from that of your samples. You will find the wavelength (λ) for maximum absorbance, and then use Beer Lambert to find absorptivity. Just plug in the numbers and solve for A, in the equation A = ecl (or A = abc as you have it). Absorption = extinction coefficient x concentration x path length