Question

When measuring the concentration of the blue dye you get a reading of 3.0 for an initial stock solution, and again after it is diluted. Explain why this result could occur

Answer 1

The beer-lambert law measures amount of radiation is being absorbed when it is passed through the solution.

This formula is the common form of the Beer-Lambert Law, although it can be also written in terms of intensities:

  

A= log₁₀(I₀/I) = Elc

Where, E= is abosorption co-efficient

c= Concentration of the solution, l= Length of the light path

In case of stock solution, the concentration of blue dye is fairly high and we see absorbance nearly 3.0. But when we dilute the solution, the moles of blue dye remains same as before( i.e as in stock solution). Therefore, the radiation passing through the solution will eventually interact with same no. of moles of blue dye in diluted solution and give absorbance nearly 3.0

Note: External effect such as temperature, pressure and protic solvent, excessive concentration of target compound will deviate the spectroscopic measurement.