Experimental Procedure

You will work in pairs for this experiment. You and your lab partner will use the Coen₂Cl₃ provided by your instrucotr to prepare 2 aqueous stock solutions of known concentrations between 0.1 and 0.2 M (you will be assigned specific concentrations in lab), and you will do a kinetic analysis of both these solutions at two different temperatures (you will be assigned two temperatures to work with in lab). At the end of the lab period the data sets from all of the different groups in lab will be pooled to create a complete data set for the kinetic analysis of the aquation reaction.

1) Prepare 30 mL of the two stock solutions you have been assigned. Use cold water to make up your solutions and keep the solutions on ice once you have prepared them.

2) Remove a small aliquot of one of these solutions and take a UV/Vis spectrum on the Ocean Optics Spectrophotometers.. Take a small sample of the aquation product (provided by your instructor) and take its UV/Vis spectrum as well.

In “scope” mode, insert your reference sample into the cuvette holder

- click on “reference”, then click on “store”

Then run a dark spectrum, by blocking the light path entirely

- click on “dark”, then click on “store”

Then switch to “absorbance” mode and insert your sample into the cuvette holder

- if you are continuously scanning, your spectrum should appear

(if not, click on “scan”)

- print out a copy of your spectrum

Once you have obtained a UV/Vis spectrum of both the starting material as well as of the product (provided by your instructor), determine the best wavelength(s) to use in doing a kinetic analysis.

3) Set up two water baths, one at each of the two temperatures that you have been assigned. It is important that the temperature of these water baths remain fairly constant (within a few degrees) over the course of the experiment - this will require some attention and creativity on your part - you may want to cool the baths down periodically by addition of cold water or ice for instance.

Once your water baths are at the correct temperatures, pour about 10 mL of your two stock solutions into two large test tubes, and place one test tube of each concentration into each of the two baths with a glass stirring rod. (Put the rest of your stock solution back on ice in case you need to do any additional runs.) You will remove aliquots from these flasks at precise intervals and record a UV/Vis spectrum. You do not need to save all the spectra, just record the absorbance at the wavelengths that you have previously selected. The higher the temperature of the water bath, the more often you will need to record spectra - your instructor will help you determine the appropriate intervals to use.

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Lab Report

From the pooled class data, you should be able to determine the order of the reaction. Once you have determined the order of the reaction, you will be able to calculate the rate constant k at a variety of temperatures, and therefore the activation energy associated with this reaction.