Law that states the linear relationship between absorbance and concentration of an absorbing species

• A. Beer-Lambert's Law
• B. Charles Law
• C. Boyle's Law
• D. Avogadro's Law

Answer: (A)

Beer-Lambert's Law describes how light absorption by a solution increases linearly with the amount of absorbing species. The relationship is A = εbc, where A is absorbance, ε is the molar absorptivity, b is the path length of the light through the sample, and c is the concentration. For a given wavelength, ε and b stay constant, so A changes in direct proportion to c. This is the basis of using a spectrophotometer to determine concentration from measured absorbance via a calibration curve. The law assumes a single, non-interacting absorber in solution and no scattering or deviations at low to moderate concentrations.

The other options pertain to gas behavior and do not describe how absorbance relates to concentration, so they don’t apply to this concept.