Question

discuss/ explain any deviation from beer lamber law

Answer 1

Beer law and Lambert law is utlizing for a solution which have relatively low amounts of solutes dissolved in it (<10mM).if concentration of solution is high (>10mM), the analyte begins to behave differently due to interactions with the solvent and other solute molecules and at times even due to hydrogen bonding interactions.

1. it has been found that at high concentrations, solute molecules possess different charge distribution on their neighboring species in the solution UV-visible absorption is well known electronic phenomenon, high concentrations would possibly result in a shift in the absorption wavelength of the analyte. At times, even electrolyte concentrations (such as those present in buffers) play an important role in altering the charge distributions and affecting UV-visible absorbance. Some large ions or molecules show deviations even at very low concentrations. For e.g. methylene blue absorptivity at 436 nm fails to observe Beer Lambert law even at concentrations as low as 10μM.
2. High analyte concentrations can also possibly alter the refractive index (η) of the solution which in turn could affect the absorbance obtained. If the addition of solute causes a significant change in the refractive index of the solution a correction to the Beer Lambert formula can be placed as:
   A = εbc (η²+ 2)²
   This correction is normally not required below concentrations of 10mM.