Beer-Lambert Law Calculator
Beer-Lambert Law Calculator
The Beer-Lambert Law Calculator is a powerful tool used to determine the concentration of a substance in a solution based on its light absorption properties.
This law, also known as Beer's Law or the Beer-Lambert-Bouguer Law, establishes a linear relationship between the concentration of a solution and its absorbance of light.
Beer-Lambert Law Chart
Concentration (mol/L) | Path Length (cm) | Molar Absorptivity (L/mol·cm) | Absorbance |
---|---|---|---|
0.001 | 1 | 5000 | 0.500 |
0.002 | 1 | 5000 | 1.000 |
0.003 | 1 | 5000 | 1.500 |
0.004 | 1 | 5000 | 2.000 |
0.005 | 1 | 5000 | 2.500 |
Beer-Lambert Law Equation
The Beer-Lambert Law is expressed by the equation:
A = εbc
Where:
- A is the absorbance (dimensionless)
- ε is the molar absorptivity (L/mol·cm)
- b is the path length of the sample (cm)
- c is the concentration of the solution (mol/L)
Let’s consider an example using this formula. Suppose you have a solution of methylene blue with a molar absorptivity of 95,000 L/mol·cm at 664 nm.
You measure its absorbance in a 1 cm cuvette and get a reading of 0.285. To find the concentration:
c = A / (εb)
c = 0.285 / (95,000 × 1)
c ≈ 3 × 10^(-6) mol/L or 3 μM
How to calculate molar absorptivity?
Molar absorptivity (ε) is a measure of how strongly a chemical species absorbs light at a given wavelength.
To calculate it, you need to rearrange the Beer-Lambert equation:
ε = A / (bc)
For example, let’s say you prepare a 0.002 M solution of potassium permanganate and measure its absorbance in a 1 cm cuvette at 525 nm.
If the absorbance reading is 0.786, you can calculate the molar absorptivity:
ε = 0.786 / (1 cm × 0.002 M)
ε = 393 L/mol·cm
This value indicates how effectively potassium permanganate absorbs light at 525 nm, which is useful for future concentration determinations or comparing the absorptive properties of different substances.
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