## The Beer-Lambert law

**Genchem laboratory I Fall 2009**

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**The Beer-Lambert law**

Many applications of the spectrophotometer are made possible by a relationship described in the Beer-Lambert law. For example, the colorimetric assay you used for measuring iron in surface waters and in breakfast cereal is based on this relationship.

For this lab session you have two tasks, both made possible by this Beer-Lambert law: Absorbance = e x concentration x path length, or more succinctly, A=eÃ¢â‚¬Â¢cÃ¢â‚¬Â¢l .

Where e is the Ã¢â‚¬Å“molar extinction coefficientÃ¢â‚¬Â Ã¢â‚¬â€œ the amount of light absorbed by a 1 M solution of a particular compound, in a particular solvent, at a particular wavelength, with a light-path (aka pathlength) of 1 cm.

- For given solutions of known composition and concentration, find the extinction coefficient for the compound in solution. That is, I give you some solutions, tell you whatÃ¢â‚¬â„¢s in them, and the concentration, and you find e.

- For solutions of known composition, and given the extinction coefficient, find the concentration of the solution. For this part, I give you solution of some compound, tell you e, and you find the concentration.

Read the accompanying discussion of the Beer-Lambert law prior to lab, and in lab youÃ¢â‚¬â„¢ll tackle tasks 1 & 2.