[palomino96]

I need help with finding out what e is?  I know that it is in L mol-1 cm-1 and the wavelength given is calculated somehow in the equation.  Can someone please help?

Shawna

[chiralic]

molar absorptivity coefficient, in older literature it is sometimes called the extinction coefficient

Chiralic

[palomino96]

Chiralic,

I know what it is called.  I have did all kind of research and searches and cannot find out what to input for e.  An example in my lab book was "The molar absorptivity of cuproine at wavelength=546nm is 6220 L mol-1 cm-1.  I cannot figure out how to break the 546nm down to get the 6220 L mol-1 cm-1.  Do you know how?

Shawna

[enahs]

You measure it analytically.

[Yggdrasil]

e is different for each substance.  You either need to measure a set of standard solutions of known concentration to determine it empirically or look it up in the literature.

[palomino96]

I am using 2.00 mL of .1 M CuSO4.  The %T=86.8, A=0.06, wavelength=700nm.  The example they are giving in my lab manual is to use formula c=A/eb.  In my case would be c=0.06/e times 1.0cm.  I feel really stupid because I know it is something that is going to seem so simple once I know how to calculate e.  Any help is really appreciated.  This is only my second chemistry class so I don't know a whole lot.

Thanks,
Shawna

[chiralic]

As wrote Yggdrasil:

You need to measure a set of standard solutions of known concentration

How? Clue: Beer's Law Plot (A vs C), check the slope (Hint: A=ebC). Also you know the
diameter of the cuvette that you are using and then you'll get "e,molar absorptivity coefficient"

Regards,

Chiralic

[chiralic]

More hint:
http://www.dartmouth.edu/~chemlab/chem6/cobalt2/full_text/write-up.html

[chiralic]

Help on line...about your post:

http://www.chm.davidson.edu/ChemistryApplets/spectrophotometry/BeersLaw.html

[enahs]

I am using 2.00 mL of .1 M CuSO4.  The %T=86.8, A=0.06, wavelength=700nm.  The example they are giving in my lab manual is to use formula c=A/eb.  In my case would be c=0.06/e times 1.0cm.  I feel really stupid because I know it is something that is going to seem so simple once I know how to calculate e.  Any help is really appreciated.  This is only my second chemistry class so I don't know a whole lot.

Thanks,
Shawna

Ok, wait.

In the equation
A = ?bc
Or as you wrote it, c = A/?b
But you know A, c and b, so solve for ?
? = A/cb

You know the concentration, just plug it in and solve for ?.

[palomino96]

So this is what I would get.
e=.06/(.1Mx1.0cm)
e=.6 mol/L cm