Question

A) Calculate the molar absorptivity constant at each concentration for all wavelengths

B) Determine which wavelength you would use to run a calibration curve for the sample and defend the answer

C) Explain why there are differences at each wavelength (if there are any) for the calculated molar absorptivity constant

Path length for all exps = 2.5 cm	Concentration	Abs @ 315 nm	Abs @ 320 nm	Abs @ 325 nm	Abs @ 330 nm	Abs @ 335 nm
	50 mM	0.08	0.12	0.23	0.20	0.18
	100 mM	0.16	0.23	0.47	0.39	0.37

Answer 1

Ans. #A. Beer-Lambert’s Law, A = e C L             - equation 1             

where,

                                    A = Absorbance

                                    e = molar extinction coefficient (M^-1cm^-1)

                                    p = path length (in cm)

                                    C = concentration

Now,

            e = A / C L

The result is tabulated below-

#B. The wavelength giving maximum value of molar extinction coefficient (e) is preferred for running the calibration curve. At this wavelength, the absorbance is maximum and there is minimum changes of error due to interfering contaminants.

Therefore, wavelength 325 nm is preferred.

#C. As wavelength differ, the energy of photon (E = hv = hc/ l ; where, E = energy, h = Plank’s constant, c = speed of light, l = wavelength). Since absorption of photons is quantized, each molecule absorbs maximum quanta of light at specified wavelength depending on the nature of the molecule.

So, due to difference in energy content, the molecule absorbs light of different wavelength at different extent leading to the difference in molar absorptivity constant at different wavelengths.