Beer-Lambert Law

Model
Beer-Lambert Law (Equation)

A = ebc (Relates the absorption of light by a solution to three variables).

Absorbance (A)

The measure of the light that is stopped or absorbed by a solution.

Molar Absorptivity Constant (e)

A constant that describes how intensely a sample of molecules or ions absorbs light of a specific wavelength (measured in L/M*cm).

Path Length (b)

The distance the light travels through the solution (usually 1 cm).

Concentration (c))

The concentration of the absorbing molecules or ions (most commonly Molarity, M).

Relationship (Absorbance and Variables)

Absorbance (A) is proportional to the path length (b) and the concentration (c) of the absorbing species.

Relationship (Absorbance and Concentration)

When b and the wavelength are held constant, the absorbance is proportional to the concentration.

Spectrophotometer/Colorimeter

A device used to measure the absorbance of a solution.

Calibration Graph

A plot of absorbance vs. concentration for standard solutions; the slope of the line is the molar absorptivity constant (eb)

Optimal Wavelength (UV/Vis)

For a colored solution, measurements should be taken at the wavelength where the absorbance is the highest (λmax); this corresponds to the complementary color.

Blank Solution

The solvent only, used to calibrate the spectrophotometer (to "tare" it) to ensure that only the absorbance of the solute is measu