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Molar extinction coefficient

Definition

noun

(spectrophotometry)

The measure of how strongly a substance absorbs light at a particular wavelength, and is usually represented by the unit M-1cm-1 or L mol-1cm-1.


Supplement

It is symbolized by ε in Beer-Lambert law, A = εcl, where A is the absorbance of the sample, l is the pathlength (usually in centimeter), and c is the concentration of the of absorbing species in the material (moles per liter).


Synonym: molar absorptivity, molar absorption coefficient, absorbancy index, absorptivity, molar absorbancy index.
See also: spectrophotometer, absorbance.


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Re: molar extinction coefficient

Well done -- I promise that the next time you face this sort of graphical calculation, it will make more sense. And as you've found, it's all about the units.

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by jonmoulton
Tue Dec 04, 2012 4:22 pm
 
Forum: General Discussion
Topic: molar extinction coefficient
Replies: 10
Views: 6921

Re: molar extinction coefficient

Yes, that sounds too low, at least for those wavelengths where methyl red absorbs strongly. Did you correct your concentrations for the dilution you made as you mixed your stock solution into liquid prior to making the spectrometer measurement?

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by jonmoulton
Mon Dec 03, 2012 4:29 pm
 
Forum: General Discussion
Topic: molar extinction coefficient
Replies: 10
Views: 6921

Re: molar extinction coefficient

... red....is this value not too small for the molar extinction coefficient though?

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by 2468
Sun Dec 02, 2012 2:38 am
 
Forum: General Discussion
Topic: molar extinction coefficient
Replies: 10
Views: 6921

pka

Hey, :) need help working this out: pH: 4 molar extinction coefficient: 0.0187142857 m-1cm-1 absorbance at 500nm: 1.492 [Acid ...

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by 2468
Fri Nov 30, 2012 10:45 pm
 
Forum: General Discussion
Topic: pka
Replies: 6
Views: 3300

Re: molar extinction coefficient

Once you have plotted the data and drawn the line, the slope is the rise/run, the dy/dx. You can count squares on the graph paper. On the other hand, you can put the values of x and y into a spreadsheet and run a linear regression. If you do that, be sure to go back to the raw data on a graph and ma...

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by jonmoulton
Wed Nov 28, 2012 11:15 pm
 
Forum: General Discussion
Topic: molar extinction coefficient
Replies: 10
Views: 6921
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