Use of Beer-Lambert Law

Use of Beer-Lambert Law

Section 1: Basics of Beer-Lambert Law

  • Beer-Lambert Law: This law relates the absorption of light by a substance to its concentration and the path length of the light.
  • Absorption of Light: It occurs when a substance absorbs photons of light, usually leading to an increase in its energy level.
  • Transmittance and Absorbance: Transmittance is the fraction of light that passes through a substance, and absorbance is a measure of the amount of light absorbed by the substance. The two concepts are inversely related.

Section 2: Components of Beer-Lambert Law

  • Concentration: The amount of a given substance in a defined volume. According to Beer-Lambert Law, the absorbance is directly proportional to the concentration of the substance.
  • Path length: The distance travelled by light through the substance. The absorbance is directly proportional to the path length.
  • Molar Absorptivity: Also known as molar absorption coefficient, it’s an indication of how strongly a substance absorbs light at a particular wavelength.

Section 3: Application of Beer-Lambert Law in Colourimetry

  • Colourimetry: This is a method used to determine the concentration of coloured compounds in a solution.
  • Use of Beer-Lambert Law: Colourimetry makes use of Beer-Lambert Law to calculate the concentration of a substance from the measured absorbance of the solution.
  • Cuvette: A small tube-like container where the solution is kept during colourimetry. The path length is the internal width of the cuvette.

Section 4: Limitations of Beer-Lambert Law

  • Limitations: Beer-Lambert Law holds true only for dilute solutions, not concentrated ones.
  • Deviations: At high concentrations, the interactions between molecules can cause deviations from the law.
  • Shifting Baselines: Other factors such as temperature and pH can cause shifting baselines, another source of deviation.

Section 5: Practical Use of Beer-Lambert Law

  • Lab Exercises: In laboratory procedures, Beer-Lambert Law is frequently used in exercises related to spectroscopy and colourimetry.
  • Determining Concentrations: It allows scientists to determine the concentrations of analytes in solutions, based on how much light they absorb.
  • Industrial Applications: The law is used widely in industrial applications ranging from biotechnology to chemical engineering and environmental science.