Question

to make beer's law plot, what will you plot?

Answer 1

Beer’s law states that the absorbance of a solution is directly proportional to the concentration of the analyte in the solution as well as the length of the solution through which light passes.

Let A be the absorbance of a solution containing an analyte at concentration c and the path length of the solution is l; therefore, as per Beer’s law,

A α c

and

A α l

Combining the two, A α c*l or A = ε*c*l where ε is the proportionality constant and is known as the molar absorptivity co-efficient of the analyte. The molar absorptivity of a solution is a property of the analyte and remains unchanged during the course of the experiment.

In most problems on Beer’s law, the path length of the solution is usually kept fixed; a standard 1 cm cuvette is used for measurements. In such situations, the absorbance of the solution is directly proportional to the concentration of the analyte. Hence, the absorbance of a series of solutions of known concentrations are plotted against the concentrations to afford a linear plot. The regression equation gives the relation between the absorbance and the concentration.

In certain cases, different volumes of an analyte having a fixed concentration are used to prepare a series of standard solutions. In such cases, the absorbance may be plotted against the volume of the solutions to get a straight line plot.