Question

The working principle of colorimeter is based on ________ law.

• A. Beer – Lambert's law
• B. Pascal's law
• C. Newton's third law
• D. Bohr's law

Answer 1

Answer:

A. Beer – Lambert's law

Beer-Lambert Law

• The colorimeter operates based on the combined principles of Beer's Law and Lambert's Law, collectively known as the Beer-Lambert Law.
• Beer's Law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species.
• Lambert's Law states that the absorbance of a solution is directly proportional to the path length (the distance the light travels through the solution).
• The mathematical representation is A = εcl, where:
  • A is the absorbance (no units).
  • ε (epsilon) is the molar absorptivity or extinction coefficient.
  • c is the concentration of the solution.
  • l is the path length of the light.
• Application in Analysis: A colorimeter measures the amount of light absorbed by a sample at a specific wavelength, allowing for the quantitative determination of solute concentrations in a liquid.
• Key Distinction: Unlike a spectrophotometer which uses a monochromator to select a specific wavelength, a colorimeter typically uses filters to select light of a specific color that is complementary to the color of the sample solution to maximize sensitivity.