12. The molar absorption coefficient for a he compound undergoes a photochemical
ID: 555907 • Letter: 1
Question
12. The molar absorption coefficient for a he compound undergoes a photochemical bleaching reaction. The product does not mol cm at 313 nm hereu 313 nm. A 1.5 x 10° M solution of the compound in a 1 cm 3 cell of l c cross-section absorb at was p ntensi laced in the path of a light beam of 0.01 mW cm at 313 nm. What fraction of the incident ty is absorbed? The absorbance (this quantity is equal to A c) decreased by 7% of the -2 riginal value in two hours. Obtain the quantum yield of the bleaching reaction.Explanation / Answer
Absorbance:
Given that
molar absorption coefficient e = 3 x 104 dm3 mol–1cm–1 = 3 x104 M–1cm–1
path length l = 0.01 cm
concentration of solution, c = 1.5 x 10-3 M
Absorbance A = ?
From Beer's law,
A = ecl
= cel
= (1.5 x 10-3 M) (3 x 104 M–1cm–1) (0.01 cm)
= 0.45
A = 0.45
Transmittance:
A= 2-log %T
0.45 = 2-log %T
%T = 35.5
% of light transmitted = 35.5
Therefore,
% of incident intensity absorbed = 100-35.5 = 64.5 %
Fraction of incident intensity absorbed = 0.645
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