Determine reaction rate and order

Determine reaction rate and order by plotting absorbance versus time.

Note

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

Procedure

1. Prepare the samples for analysis.

   1. Fill the cuvettes ¾ full with the sample solutions and cap.

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

      Note

      Handle the cuvettes by the lined sides to avoid getting fingerprints on the smooth sides.

2. Calibrate the spectrometer.

   1. Select the Analyze Solution page .
   2. Cover the spectrometer to block ambient light and click .
   3. Insert the reference solution into the spectrometer, then click .

3. Select an Analysis Wavelength.

   1. Place the most concentrated solution to be analyzed into the spectrometer, then click Record .
   2. In the tools panel, adjust the smoothing and number of scans to average as needed.
   3. Click Stop when you are satisfied with the results.
   4. Drag the coordinate tool on the graph to the wavelength you want to analyze. This is usually a high point on the curve.
   5. Once you have found a desirable wavelength, click .

4. Collect data.

   1. Select the Time page from the top of the screen.
   2. Place the sample solution into the spectrometer and click again.
   3. Click to rescale your data. After allowing enough time for the reaction to take place, click again.

5. Analyze the data.

   1. Click to remove the Live Scan Display from the graph.
   2. Click to create a best fit line and display the equation for the line.
   3. Click on the y-axis to cycle the between Absorbance, ln(Absorbance), and 1/Absorbance to find a linear trend. Use the results to determine the order of reaction.

Classroom Ready Experiments

Kinetics of Crystal Violet Fading

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 determined by the student. Crystal violet fading is investigated using different concentrations of sodium hydroxide.

Enzyme Activity

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