CHEM 211 Laboratory Chemical Kinetics

Reference: General Chemistry Laboratory Experiments, Suzanne W Slayden, 1999, 3rd edition, Pages 137-143.

Purpose: The purpose of this experiment is to determine rate constant for a chemical reaction.

Procedure and Observations: Do preliminary calculations as instructed in the lab manual. Record all your data in your laboratory notebook as you proceed with the experiment.

Data: After you have measured the temperature and all the times and absorbances, enter your own data into the appropriate Web-based data entry form, using a computer in the lab. In your measurements and calculations, remember to pay attention to uncertainties and significant figures.

Results: Outside of class, retrieve your data in spreadsheet form (along with that of the entire class) from: http://chem.gmu.edu/results/. Then use Excel to calculate the densities of the various diluted solutions, stock solution and water.

Your lab report should include the following in addition to the pages from your lab notebook:  An Excel sheet “Raw Data” showing the raw data for the entire class (as downloaded).  A 2nd Excel sheet “Class Results” showing the calculated results for each student in the class – each in a separate row. The columns should include: o the elapsed times (in minutes) at which absorbances were measured o the ln(A) for each absorbance A, in the same order as the times o the slope and intercept for the ln(A) vs. time. Use the Excel functions =SLOPE(y-range, x-range) and =INTERCEPT(y-range, x-range). Note that the time values are the x-range and the ln(A) values the y-range. o the rate constant  A 3rd Excel sheet “My Results” showing your own results, only. There will be one row for each of your absorbance measurements. There should be two columns: o elapsed (minutes) o ln(A)  An Excel chart of ln(A) vs. time for your own data only, based on the “My Results” sheet described above. ln(A) should be on the y-axis and time on the x-axis. Include a linear regression fit to your points and show the equation of the line on the chart. Format your chart so that it looks like the Web example at: http://chem.gmu.edu/results/samples/Density_sample_charts/density.htm

Discussion: In your discussion section address the following points:  Why is it important to remove the sample from the spectrometer in between measurements?  Explain any deviations from linearity in your ln(A) vs. time plot.  What are the possible sources of error that could account for any difference in your value and the true rate constant value?  How consistent are the values of the rate constant obtained by the class? What is the standard deviation of the rate constants from the mean?