Beer's Law Spectrophotometer Lab

Instructions

Zero the spectrophotometer, measure standards of known concentration to build a calibration curve, then measure an unknown and calculate its concentration.

  1. Zero the instrument with a blank, then measure standards with known concentrations.
  2. Use the calibration curve to find the concentration of the unknown sample.
  3. Record your measurements and explain the relationship between concentration and absorbance.

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1.00 cm cuvettes. Readings have a little noise, like a real instrument.

2. Measure

The spectrophotometer

Spectrophotometer
Absorbance
Transmittance
Wavelength
In the cuvette

Blank

Unknown

3. Graph

Calibration curve

4. Analyze

Find the unknown

Your data

SampleConcentration (M)AbsorbanceRemove

The unknown

5. Make sense of it

What does the curve tell you?

Try a wavelength far from λmax and build the curve again. Then try standards above an absorbance of 1.5.

Why is the calibration curve a straight line? What does its slope tell you? Why is it best to measure at λmax, and to keep the unknown between your standards?

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