Question

According to Beer’s Law, if the absorbance of a sample is 0.33 at a concentration of 0.20M, what is the absorbance at a concentration of 0.40M?

Answer 1

Well, Beer's law gives you a straight line. Would the absorbance not be twice?

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If a `"0.20 M"` solution had an absorbance of `0.33`, then doubling the concentration doubles the absorbance to `0.66`.

Beer's law is given by:

`A = epsilonbc`

and so, if you plot absorbance `A` vs. concentration `c`,

you get the slope `epsilonb`, where `epsilon` is the molar absorptivity in `"L/mol"cdot"cm"` and `b` is the path length of the cuvette in `"cm"`.

The molar absorptivity is an intrinsic property of the analyte, so it won't change with analyte concentration.

CHALLENGE: From these two data points, calculate the molar absorptivity of the analyte in your solution for a path length of 1 cm.