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Determine order of reaction

Determine order of reaction by plotting absorbance versus time.

Note

For a more detailed experiment procedure, see the Kinetics sample experiment. Classroom-ready experiments are also available in the PASCO Experiment Library.

Procedure

Part 1: Prepare the samples for analysis

  1. Fill the cuvettes ¾ full with the sample solution, then cap the cuvettes.

  2. Prepare a reference solution by filling one cuvette ¾ full with the solvent used to make the sample solutions, then cap the cuvette.

    Note

    Handle the cuvettes only by the lined sides to avoid getting fingerprints on the smooth sides, which could interfere with the results.

Part 2: Connect and calibrate the spectrometer

  1. Start Chemvue, then connect your spectrometer to the program. The software should automatically open to the solution spectra page of the Spectrometry Module.
  2. Ensure the spectrometer's sample chamber is covered to block all ambient light, then select Calibrate Dark .
  3. Insert the reference solution cuvette into the spectrometer's sample chamber, then select Calibrate Reference .

Part 3: Select an analysis wavelength

  1. Place the most concentrated solution to be analyzed into the spectrometer, then select the Start button.
  2. In the Tools panel, adjust the Smoothing and Number of Scans to Average sliders as needed.
  3. Once you are satisfied with the results, select Stop .
  4. Click the Select Wavelength tool, then drag the coordinate data target on the graph to the wavelength you want to analyze. This will usually be a high point on the curve.
  5. Once the data target is at the desired wavelength, select the target again and click the floating Select Wavelength icon.

Part 4: Collect data

  1. Switch to the concentration change over time page using the navigation bar.
  2. Place the sample solution to be studied into the spectrometer, then select Start again to begin collecting data.
  3. Select Scale to Fit to rescale your data.
  4. After allowing enough time for the reaction to take place, select Stop again to end data collection.

Part 5: Analyze the data

  1. Select Toggle Live Scan Display to remove the live scan display from the graph.
  2. Select Linear Fit to create a best fit line and display the equation for the line.
  3. Use the Quick Calcs tool on the y-axis to cycle the measurement between Absorbance, ln(Absorbance), and 1/Absorbance until you find a linear trend. Use the results to determine the order of the reaction.

Classroom-ready experiments

Kinetics of Crystal Violet Fading (Spectrometer)

Students determine the reaction order of crystal violet fading in the presence of sodium hydroxide. A calibration curve of crystal violet is generated and optimal absorbance wavelength is determined by the student. Crystal violet fading is investigated using different concentrations of sodium hydroxide.

Enzyme Activity (Spectrometer)

Students use a spectrometer to investigate the catalyzed breakdown of hydrogen peroxide by peroxidase.