An unknown was prepared with the concentration of 0.000630 M. A Beer's Law plot was prepared using the absorbance values from standard solutions of ASA and a line drawn through all the points passed through the origin with a slope of 1550.2 M–1. The expected absorbance and %T values for the diluted aspirin solution prepared by the student is
and , respectively.
1 answer

The Beer's law plot is usually absorbance (y axis) against concentration (x axis) so the slope is
absorbance (no units)/concentration (mol litre1)
so the units of the slope are litre mole1
Thus to find the absorbance of an unknown we need to multiply the concentration of the unknown (0.000630 mole litre 1) by the slope (1550.2 litre mole1). The units will cancel to give no units which is in reality 'absorbance'.