BEERS LAW

1. Key Takeaways: Beer's Law

Beer's Law states that the concentration of a chemical solution is directly proportional to its absorption of light.

The premise is that a beam of light becomes weaker as it passes through a chemical solution. The attenuation of light occurs either as a result of distance through solution or increasing concentration.

Beer's Law goes by many names, including the Beer-Lambert Law, Lambert-Beer Law, and Beer-Lambert-Bouguer Law.

2. Equation for Beer's Law

Beer's Law may be written simply as:

A = εbc

where A is absorbance (no units)

ε is the molar absorptivity with units of L mol-1 cm-1 (formerly called the extinction coefficient)

b is the path length of the sample, usually expressed in cm

c is the concentration of the compound in solution, expressed in mol L-1

Calculating the absorbance of a sample using the equation depends on two assumptions:

The absorbance is directly proportional to the path length of the sample (the width of the cuvette).

The absorbance is directly proportional to the concentration of the sample.

3. How to Use Beer's Law

While many modern instruments perform Beer's Law calculations by simply comparing a blank cuvette with a sample, it's easy to prepare a graph using standard solutions to determine the concentration of a specimen. The graphing method assumes a straight-line relationship between absorbance and concentration, which is valid for dilute solutions. 

4. Importance of Beer's Law

Beer's Law is especially important in the fields of chemistry, physics, and meteorology. Beer's Law is used in chemistry to measure the concentration of chemical solutions, to analyze oxidation, and to measure polymer degradation. The law also describes the attenuation of radiation through the Earth's atmosphere. While normally applied to light, the law also helps scientists understand the attenuation of particle beams, such as neutrons. In theoretical physics, the Beer-Lambert Law is a solution to the Bhatnagar-Gross-Krook (BKG) operator, which is used in the Boltzmann equation for computational fluid dynamics.