In the Beer-Lambert law, what does the symbol c represent?

• A. Concentration (mol/L)
• B. Absorbance
• C. Path length
• D. Molar absorptivity

Answer: (A)

In the Beer-Lambert law, how much light is absorbed depends on how many absorbing molecules are in the path and how far the light travels through the sample. The symbol c represents the concentration of the absorbing species in the solution, typically expressed in moles per liter. The law is A = εlc, where ε is the molar absorptivity, and l is the path length, so c is the variable that scales absorbance with how much of the absorbing substance is present. Absorbance itself is a unitless quantity derived from the light intensities, while path length and molar absorptivity are the distance the light travels and a property of the specific substance at a given wavelength, respectively.