Beer-Lambert Law Verification

Demonstrating the linear relationship between absorbance and concentration

Colorimetry Intermediate (High School) 60 min ~$12.00

Objective

Verify the Beer-Lambert law by measuring the absorbance of CuSO₄ solutions at various concentrations and constructing a calibration curve.

Background

The Beer-Lambert law states that absorbance is directly proportional to both the concentration of the absorbing species and the path length of the sample (A = εbc). By preparing a series of standard solutions of known concentration and measuring their absorbance at a fixed wavelength, students construct a calibration curve. This curve can then be used to determine the concentration of unknown samples — a technique fundamental to analytical chemistry.

Safety Warnings

  • CuSO₄ is an irritant — avoid skin contact
  • Do not pipette by mouth
  • Wipe cuvettes with lint-free tissue before measurements
  • Dispose of CuSO₄ solutions in inorganic waste

Required PPE

goggles lab_coat

Materials

  • Copper sulfate (CuSO₄·5H₂O) (10 g)
    For stock solution
  • Distilled water (500 mL)
    Solvent
  • Unknown CuSO₄ solution (50 mL)
    Prepared by instructor

Equipment

Colorimeter or spectrophotometer Cuvettes (matched pair) Volumetric flasks (100 mL, 6 total) Pipettes (10 mL, 25 mL) Pipette filler Graph paper or computer

Procedure

1

Prepare a 0.5M stock solution by dissolving 12.5 g CuSO₄·5H₂O in distilled water and making up to 100 mL.

5 min
2

Prepare standard solutions by dilution: 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 M. Label each flask clearly.

10 min
3

Set the colorimeter to 635 nm (red filter) — the maximum absorbance wavelength for blue CuSO₄ solutions.

3 min
4

Zero the instrument using a cuvette of distilled water (blank). Ensure the cuvette is clean and properly oriented.

2 min
5

Measure and record the absorbance of each standard solution, starting from the most dilute. Rinse the cuvette between samples.

15 min
6

Measure the absorbance of the unknown solution.

5 min
7

Plot absorbance (y-axis) vs. concentration (x-axis). Draw the best-fit line and determine the unknown concentration from the graph.

20 min

Expected Results

The plot should show a linear relationship (straight line through the origin) for the standard solutions. The unknown concentration is read from the x-axis at the corresponding absorbance on the calibration curve.

Cleanup

Pour CuSO₄ solutions into the inorganic waste container. Rinse all volumetric flasks and cuvettes with distilled water.

Details

Category
Colorimetry
Difficulty
Intermediate (High School)
Duration
60 min
Est. Cost
$12.00
Steps
7
Materials
3

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Frequently Asked Questions

What is the objective of Beer-Lambert Law Verification?
Verify the Beer-Lambert law by measuring the absorbance of CuSO₄ solutions at various concentrations and constructing a calibration curve.
How difficult is Beer-Lambert Law Verification?
This experiment is rated as Intermediate (High School). It takes approximately 60 minutes to complete.
What safety precautions are needed for Beer-Lambert Law Verification?
Key safety precautions include: CuSO₄ is an irritant — avoid skin contact; Do not pipette by mouth; Wipe cuvettes with lint-free tissue before measurements.
What materials are needed for Beer-Lambert Law Verification?
The main materials required are: Copper sulfate (CuSO₄·5H₂O), Distilled water, Unknown CuSO₄ solution.
What results should I expect from Beer-Lambert Law Verification?
The plot should show a linear relationship (straight line through the origin) for the standard solutions. The unknown concentration is read from the x-axis at the corresponding absorbance on the calibration curve.