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?

1 Answer
May 9, 2018

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


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#,

http://www.scienceteacherprogram.org/

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.