J.R. S. answered • 09/30/17
Tutor
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Ph.D. in Biochemistry--University Professor--Chemistry Tutor
This is a problem involving the use of Beer's Law
A = ecl
A = Absorbance
e = extinction coefficient (molar absorbtivity)
c = concentration in moles/liter
l = path length in cm (usually 1cm or assumed to be 1cm)
There isn't sufficient information provided to calculate molar absorbtivity because one does not know the absorption or the molar concentration.
J.R. S.
tutor
With this additional information, you can calculate a "pseudo" molar extinction coefficient. It isn't a "real" molar absorbtivity, because you are using units of mg/ml as concentration instead of using moles/liter (M). If you know the molar mass (molecular weight) of the dyes, you can convert to M and get a real molar absorbtivity. Also, the λmax is not involved in calculating molar absorbtivity.
Blue λmax is 630: 0.7 = e x 40 mg/L x 1 cm and e = 0.7/40 = 0.0175
Red λmax is 520: 2.3/60 = 0.038
Red λmax is 500: 2.1/70 = 0.03
Report
10/01/17
Sonia B.
Can you conclusively tell the two red dyes apart using this technique? Explain how the differences in λ
max between the red and the blue dyes relate
to the different colours of the dyes?
max between the red and the blue dyes relate
to the different colours of the dyes?
Report
10/29/17
J.R. S.
tutor
I would say that you CANNOT conclusively tell the red dyes apart. Their λmax values are too close, and they have essentially the same extinction (0.038 v. 0.03).
The color of the dyes (red v. blue) is related to their chemical structure and this in turn affects how light is absorbed. When white light passes through a colored substance, a certain portion of the mixed wavelengths is absorbed. The remaining light will then assume the complementary color to the wavelength(s) absorbed. So, if 500 λ wavelength is absorbed, the color will be predominantly red and if 600 λ wavelength is absorbed the color is predominantly blue.
Report
10/29/17
Sonia B.
09/30/17