EXPERIMENT 2
AIM: Determination of the Concentration of an Unknown KMnO4 Solution by
colorimetrically.
THEORY: The Beer-Lambert law states that the absorbance of a solution is directly
proportional to the concentration of the absorbing species in the solution and the path
length. Thus, for a fixed path length (cuvette length), Visible spectroscopy (colorimetry)
can be used to determine the concentration of the absorber in a solution. The absorbance
changes with concentration, A higher concentration of the colored solution absorbs more
light (and transmits less) than a solution of lower concentration.
According to Beer–Lambert law,
log ( I o / I t ) = A= ε c l
where
I o and I t are the incident and transmitted intensities,
A = absorbance and
ε is a constant i.e. absorptivity (formerly called the extinction coefficient ). If the
concentration is measured in molL−1 , the absorptivity is called the molar
absorptivity .
A= ε c l
At constant length of solution
A α c
REQUIREMENTS
Colorimeter, cuvette, six test tubes
Two Burettes or graduated cylinders two 100 mL beakers
0.01M KMnO4 solution
distilled water, test tube rack, stirring rod, tissues (preferably lint-free)
