how do you get the molar absorptivity (beer lambert's law)?

Question

i'm about to use the beer lambert's law for the equation Fe3+ + SCN- <==> [FeSCN]2+. i already have the absorbance and pathlength. we are asked to get the concentration but then i dont know how to get the molar absorptivity. please help!

Answer 1

Beer's Law :

Let I be the intensity of light passing through a substance, then

where l is the length (in cm), c in the molar concentration (in M), and is the molar absorptivity (in cm-1 M-1).

Answer 2

Molar absorptivity of a substance is usually constant, and in getting the unknown concentration, this is not usually included. Concentrations can be derived by using:

1. Ratio of standard to unknown with the formula:

Concentration of Unknown (Cu) = Absorbance of Unknown X Concentration of standard solution divided by the Absorbance of the standard solution. ( notice that the molar absorptivity is not used.)

2. Standard Curve - plot a curve making use of two or more standard values in a graphing paper and then extrapolate the absorbance of the Unknown solution to get the concentration.

I advise you to use method no. 1 . Where all the data you need are only the absorbance of both unknown and standard and the standard concentration (this can be seen in the standard bottle itself)

Answer 3

RE: applying the Beer-Lambert regulation, calculate the molar extinction coefficient (molar absorptivity cost) for the.....? copper complicated in a answer having a concentration of 0.815 mg/mL. the path length is a million.0 cm and the absorbance cost is 0.7729. Your units could be (mg/mL)-a million cm -a million.