Beer's Law: A 33.8 mg/l solution of compound A exhibited an extinction of 0.67 at 520 nm. Calculate the concentration of compound A when the extinction is 0.33 at 520nm.

I understand that A=e*c*l

and I know that c must be in mol/l

since the concentration is in mg/l, I have no idea on how to do this.

Question

Beer's Law: A 33.8 mg/l solution of compound A exhibited an extinction of 0.67 at 520 nm. Calculate the concentration of compound A when the extinction is 0.33 at 520nm. 

I understand that A=e*c*l 

and I know that c must be in mol/l 

since the concentration is in mg/l, I have no idea on how to do this.

aaronq · Answer

$Abs=\epsilon*l*C \rightarrow Abs= 0.67*(1)*33.8 mg/l $

you need the absorbance with the new $\epsilon$ or are we assuming that it remains the same?

jfraser · Answer

the concentration can be in ANY unit, so long as you keep it constant. The value of $\epsilon$ won't be in the "right" units, but the relationship is still going to work. Find the value of $\epsilon$ using the first set of data, then plug in the second set to find the concentration of the unknown.