Chemistry

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Beer-Lambert Law Calculator.

Calculate absorbance from molar absorptivity, path length, and concentration.

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Absorbance: 1 AU

Absorbance

1.000000AU

Educational formula calculator. Keep units consistent; chemistry procedures, concentrations, and safety decisions require qualified laboratory guidance. Never mix cleaning products.

Use Cases

Spectrophotometry Analysis

Determine the absorbance of a solution for quantitative analysis in chemistry labs, such as measuring concentration of a known compound.

Example: If ε = 1500 L·mol⁻¹·cm⁻¹, l = 1 cm, c = 0.002 mol/L, then A = 3.0.

Quality Control in Pharmaceutical Industry

Verify the concentration of active ingredients in drug formulations by measuring absorbance and using known molar absorptivity values.

Example: Check if a batch meets spec by comparing calculated absorbance to expected range.

Frequently Asked Questions

What is the Beer-Lambert Law?
The Beer-Lambert Law relates the attenuation of light to the properties of the material through which it travels. It states that absorbance (A) equals the product of molar absorptivity (ε), path length (l), and concentration (c): A = εlc.
What units are used in this calculator?
Molar absorptivity is in L·mol⁻¹·cm⁻¹, path length in cm, and concentration in mol/L. The resulting absorbance is unitless.
Can I use this calculator for any wavelength?
Yes, as long as you know the molar absorptivity at that specific wavelength. Molar absorptivity is wavelength-dependent, so ensure you use the correct value for your measurement.

Tips & Common Mistakes

Tips

  • Ensure the concentration is in mol/L; convert from other units like mg/mL using molar mass.
  • Path length is typically 1 cm for standard cuvettes, but verify your cuvette's path length.
  • Molar absorptivity values are wavelength-specific; use the correct value for your measurement wavelength.
  • For accurate results, keep absorbance values between 0.1 and 1.0 to minimize errors.

Common Mistakes to Avoid

  • Using concentration in units other than mol/L without conversion.
  • Confusing molar absorptivity with extinction coefficient; they are the same but ensure units match.
  • Forgetting that path length must be in cm; if using mm, convert to cm.

Last updated: August 13, 2026