What is the significance of the molar extinction coefficient

What is the extinction coefficient? The proportion of the light absorbed will depend on how many molecules it interacts with. Suppose you have got a strongly colored organic dye. If it is in a reasonably concentrated solution, it will have a very high absorbance because there are lots of molecules to interact with the light. However, in an incredibly dilute solution, it may be very difficult to see that it is colored at all.

The absorbance is going to be very low. Suppose then that you wanted to compare this dye with a different compound. Unless you took care to make allowance for the concentration, you couldn't make any sensible comparisons about which one absorbed the most light. The absorption coefficient of a glycogen-iodine complex is 0.

Suppose this time that you had a very dilute solution of the dye in a cube-shaped container so that the light traveled 1 cm through it. The absorbance is not likely to be very high. On the other hand, suppose you passed the light through a tube cm long containing the same solution. More light would be absorbed because it interacts with more molecules. Again, if you want to draw sensible comparisons between solutions, you have to allow for the length of the solution the light is passing through.

Path length is usually considered to be 1. Concentration of the substance c should also be known. Again here path length will be 1. Thus, the slope will give you the molar absorptivity. Calculators are the easiest way to calculate these values. E with immersion solvent, immersion time, immersion concentration respectively.

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