Experiment 20: Beer’s Law General Chemistry I and II Lab Manual Dakota State University page 206 of 232 lc A e = where A is absorptivity, ε is the absorptivity coefficient which is a constant for any given chemical (it’s why one chemical is darker at the same concentration as another), l is path length of light through the solution (which we work very hard to keep constant during these studies so ε l=constant), and c is the concentration of the chemical. Because concentration is linear with absorptivity, and absorptivity is logarithmic with respect to percent transmittance, chemists, who are just as lazy a bunch as anybody else, much prefer using absorption for spectroscopic measurements so we don’t have to worry about working with logarithms in our calculations, despite the fact that it might be a little bit more intuitively simple to think of amount of light getting through the solution rather than the amount of light absorbed by the solution. Experiment:
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