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The Beer-Lambert Law, also known as Beer’s Law, is a fundamental principle in spectroscopy that describes the relationship between the absorption of light and the concentration of a solute in a solution. It is widely used in chemistry and physics to determine the concentration of substances in solution by measuring the amount of light absorbed at a particular wavelength.
Mathematical Expression of the Beer-Lambert Law
The Beer-Lambert Law is mathematically expressed as:
A = ε c l
Where:
- A = Absorbance (no units)
- ε = Molar absorptivity or extinction coefficient (L·mol⁻¹·cm⁻¹)
- c = Concentration of the solute (mol·L⁻¹)
- l = Path length of the solution (cm)
Our calculator automatically calculates all the variables when the known values are entered in their respective fields.
Interpretation of the Formula
The Beer-Lambert Law shows a direct relationship between the absorbance of light and the concentration of the solution. Absorbance is the extent to which a substance absorbs light at a given wavelength. The molar absorptivity (ε) is a constant that indicates how strongly the substance absorbs light at a particular wavelength, and it depends on the chemical nature of the solute and the wavelength of the incident light.
The concentration of the solute (c) and the path length (l) are also factors in determining absorbance. If either the concentration or the path length increases, the absorbance will increase proportionally, assuming other factors remain constant.
Limitations of the Beer-Lambert Law
While the Beer-Lambert Law is a useful tool, it has certain limitations:
- At very high concentrations, the law may no longer hold due to interactions between molecules that affect absorption.
- At high concentrations, scattering of light by particles in the solution can cause deviations from the law.
- Imperfections in the spectrophotometer, such as stray light, can result in inaccurate measurements.
