1. Beer’s Law P0 Uses of Beer’s Law
- Relates concentration to the optical measurement of ‘absorbance’
- combined with spectrophotometry can be used to distinguish and compare different molecules in solution

2. The relationship between absorbance and transmittance is illustrated in the following diagram:
0% %
Absorbance

3. The amount of radiation absorbed may be measured in a number of ways:
Transmittance, T = P / P0 % Transmittance, %T = 100 T
Absorbance,
A = log10 P0 / P A = log10 1 / T A = log10 100 / %T A = 2 - log10 %T 

4. Question : Why do we prefer to express the Beer-Lambert law using absorbance as a measure of the absorption rather than %T ?
Compare the two equations that we use:
A=abc
%T = 100 P/P0 = e -abc

5. Compare how each equation Graphs

6. Beer’s Law Equation
A=abc Where, a= molar absorptivity (is a measure of the amount of light absorbed per unit concentration; this value is a constant for a given solution) b = cell path length (usually 1cm) (Cuvette) c = concentration (M) A = abc Where ab = constant, then A = constant times c So when we plot this y=mx+b

7. Beer’s Law
In order to use A = abc, we need to define values for a and b. b = path length – “blank” – distilled water in a cuvette a = colorimeter(select a preset wavelength) spectrophotometer (choose wavelength where maximum absorption of photons occurs)