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ENVE 201 Environmental Engineering Chemistry 1 . COLORIMETRY Dr. Aslıhan Kerç. Colorimetry. Colorimetric methods are applicable to dilute solutions. For a colorimetric method to be quantitative, it must form a coumpound with definite color characteristics.
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ENVE 201EnvironmentalEngineeringChemistry 1 COLORIMETRY Dr. Aslıhan Kerç
Colorimetry • Colorimetric methods are applicable to dilute solutions. • For a colorimetric method to be quantitative, it must form a coumpound with definite color characteristics. • Color amount must be directly proportional to the concentration. • Colored compound must obey Beer’s Law and Lambert’s Law.
Lambert’s Law • Relates the absorption of light to the depth or thickness of the colored liquid. • Each layer of equal thickness absorns an equal fraction of the light which traverses it. • Monochromatic light?
Lambert’s Law • Intensity decreases exponentially with length. • This law is valid for homogeneous solutions I Io Cell length l
Lambert’s Law l: length of absorbing layer T: transmittance of solution A: Absorbance or optical density k’ : constant for particular solution I Io Cell length l
Beer’s Law Intensity of a ray of monochromatic light decreases expponentially as the concentration of the absorbing medium increases. k’’ : constantforparticularsolution C: concentration
Beer’s Law If light is absorbed exponentially with concentration, the colored material is said to confirm Beer’s Law. Prepare a series of samples in desired concentration range, measure light transmission. If it forms a straight line on a semi-log paper obeys Beer’s law
Lambert – Beer Law Two absorbtion laws are combined:
