| Computer-Interfaced
Experiments - Absorbance Measurement Acid-catalyzed Iodination of Acetone - Pseudo Zero Order Reaction Objectives: Determination of Rate Constants, Test for a Pseudo Zero Order Reaction Peter Keusch | ||||||||||||||||||||||||||||||
IBK electronic + informatic IBK electronic + informatic German version 
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Fig. 1: Experiment set-up |
7 mL of 0.5 molar sulfuric acid are pipetted into a 50 mL graduated cylinder and via a burette the calculated volume of acetone is added. Afterwards the acid acetone solution is accurately made up to a volume of 46 mL with distilled water. Now the solution is poured into a beaker. 4 mL of 0.05 molar iodine solution are pipetted into a further beaker. The top of the beaker is covered with a piese of parafilm foil. The plastic film is firmly fastened around the mouth of the beaker to prevent the release of iodine into the air. The two beakers are placed in a thermostated water bath at approx. 35°C (temperature within the sample compartment of the photometer) and left there about 15 minutes until thermal equilibrium to be reached. During the thermal equilibration period the photometer is calibrated and the program Chemex is matched (see above). After thermal equilibrium has been reached the reaction temperature is read to nearest 0.1 °C. The acetone solution is poured smoothly and rapidly to the iodine solution. A cuvette is filled about 3/4 full with the reaction solution. The cuvette covered with a bit of Parafilm, is inverted 2-3 times to ensure proper mixing and placed into the light-tight sample compartment of the photometer. Simultaneously the sensing software is started. The change in transmittance and in absorbance is displayed simultaneously on the measuring screen (Fig. 2). The in-situ determination of the reaction rate on the basis of a continuous logging of photometrical data is allowed in rapid reactions (small change in temperature during te reaction). |
