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AP Chemistry 3.13.A: Beer-Lambert Law

Explore AP Chemistry 3.13.A questions on using absorbance and calibration data to determine concentration and select wavelengths for spectrophotometry.

Syllabus
Effective Fall 2025
Course
AP Chemistry

Exam points

  • Explain how catalysts alter pathways and activation energy without changing overall reaction thermodynamics.
  • Apply energy profiles and mechanistic models to predict catalyst effects on reaction rates.

3.13.A—Explain the amount of light absorbed by a solution of molecules or ions in relationship to the concentration,… question 1

[Maximum number: 2]

A student wants to determine the concentration of permanganate, MnO4−(aq)\mathrm{MnO}_{4}{ }^{-}(a q), in a solution. The student plans to use colorimetric analysis because solutions containing MnO4−(aq)\mathrm{MnO}_{4}{ }^{-}(a q) have a purple color.

Figure for Question 3.13.A—Explain the amount of light absorbed by a solution of molecules or ions in relationship to the concentration,… question 1 — AP Chemistry

Question (a)

(a)

To determine the optimum wavelength for an experiment that measures the concentration of MnO4−(aq)\mathrm{MnO}_{4}^{-}(a q), the student takes a sample of the solution and measures the amount of light absorbed by the sample over a range of wavelengths. The data are plotted in the graph shown. Identify the optimum wavelength that the student should use for the experimental procedure.

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Question (b)

(b)

Assuming that all lab equipment is functioning properly, identify which one of the procedural steps the student could have executed incorrectly that would explain why the marked data point is below the line of best fit. Justify your answer.

Figure for Question (b) — AP Chemistry
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