Various wavelengths are used to calculate the absorbency value for a concentrati

Question

Various wavelengths are used to calculate the absorbency value for a concentration. Volumes remain the same. The only thing that changes are the wavelengths used by different experimenters. Will the different wavelengths produce or have any impact on the calculated equilibrium constant Kc for the reaction that occurs prior to the reading of the absorbency? Comment on Beer's Law relationship to this if possible.

[I can give you the reaction if necessary but i believe this is a concept question].

Thank you.

Explanation / Answer

Each substance have a spectrum which show maximum and minimum peaks of absorption, even more if you have an equilibrium where you have reactants and products. Each one will have its own spectrum. Thus you will be really observing a sum of both, the spectra of the reactant and the products. If you change the wavelenght you are not chaging the Keq of your reaction, but you could observe different species if they are present. If the product have color and the reactants not, the process is easy. In that case you can use whatever wavelenght where the product absorbs and calculate the Keq. So if both reactant and products absorbs you have to take a wavelength where each one does not interfere each other. If you take a zone where there is interference the Keq will be wrong.

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