Question

Given that the maximum molar absorption coefficient of a molecule containing a carbonyl group is 30 dm3mol−1cm−1 near 280 nm, calculate the thickness of a 1.0 mM sample that will result in

a. Half the initial intensity of radiation;

b.One tenth the initial intensity.

Answer 1

1. Half the initial intensity of radiation means T= I/I_o = 0.50

     The sample absorbance is

      A= log(1/T) = log 2 = 0.301

Than use the Lambert-Beer’s law:

A = ε C l

l = A/( ε C) =

   = 0.301/ (30 dm³mol⁻¹cm⁻¹ x 1x10^-3 mol.dm^-3) =

   = 0.301/0.030 cm⁻¹ = 10 cm

1. T = I/I_o = 0.10

        A= log(1/T) = log 10 = 1.00

      l = A/( ε C) = 1.00/0.030 cm⁻¹ = 33.2 cm