Question

Which is true for spectroscopy of a mixture?

A. The absorbance for a mixture at a particular wavelength is the sum of the absorbances for the components that absorb at the particular wavelength.
B. Spectrophotometers can differentiate between mixture components that absorb at the same wavelength.
C. Each component in a mixture has the same molar absorptivity at the same wavelength.
D. The concentration for each component in the mixture is easily calculated with a set of simultaneous equations if there is significant overlap of individual spectra.
E. The concentration for each component in a mixture is easily calculated by least squares for guesses of each component when the individual spectra are well resolved.

Answer 1

Absorbance of a mixture solution is additive. That mean the total absorbance at a perpendicular wavelength is the sum of the absorbance of its components at that wavelength.

This can be demonstrated through the sum of the absorbance in the solutions for which it is necessary to add to each specific absorbance its respective wavelength. Mathematically this is:

$A_{total,\lambda} = \sum\limit_i A_{i,\lambda}$

$A_{total,\lambda} = A_{1,\lambda}+A_{2,\lambda}+A_{3,\lambda}+...$

Therefore the correct option is A.