Chemical Kinetics 1 Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Preparing for a kinetics run Before starting a reaction, you will need to bring all the reactants to a constant temperature in an insulated beaker. Make a copper wire holder for your spectrometer cuvet, so it can stay in the constant temperature bath between absorbance readings. A piece of tape around the top of the cuvet will keep it from falling into the bath. The beaker should be filled about three-quarters full with a suitable mixture of hot and cold water to achieve a constant temperature near 25°C, measured as accurately as possible with the thermometer in your drawer. If your water bath is full when you arrive, measure its temperature and check the temperature stability, rather than starting over with fresh water. Record the water bath temperature, since you will need it next week. The 50 mL Erlenmeyer flask containing all the reagents except the triiodide solution should be suspended in the bath on a loop of copper wire. About ten minutes is sufficient to assure good temperature equilibration. A stoppered test tube containing about 15 mL of triiodide solution should also be thermostated in your water bath. Once all the reagents are at constant temperature, the necessary volume of triiodide solution should be added to the 50 mL flask with a 2 mL pipet, using a pipet bulb. The addition of the triiodide defines the starting time (t = 0) for the reaction. Be sure to stir the solution thoroughly with a glass stirring rod after addition of the triiodide. An aliquot of the solution should be transferred to a cuvette that is also suspended in the bath in your copper wire holder. Absorbance measurements should be made as quickly as possible, removing the cuvette from the bath, wiping it dry, taking the reading at 565 nm and returning it to the bath, all in a few seconds. Another cuvette with water in it should be used to re-zero the colorimeter between readings.
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