experiment_five - Iodine Clock Reaction Experiment Five...

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Iodine Clock Reaction Experiment Five Chemistry M01B Laboratory Manual pp. 22 Chemical Kinetics: Iodine Clock Reaction In the previous experiment, we discussed the factors that influence the rate of a chemical reaction and presented the terminology used in quantitative relations in studies of the kinetics of chemical reactions. That material is also pertinent to this experiment and should be studied before you proceed further. This experiment involves the study of the rate properties, or chemical kinetics, of the following reaction between iodide ion and bromate ion under acidic conditions: 6 I - (aq) + BrO 3 - (aq) + 6 H + (aq) 3 I 2 (aq) + Br - (aq) + 3 H 2 O(l) (1) This reaction proceeds at an easily measurable rate that depends on the concentrations of the I - , BrO 3 - , and H + ions according to the rate law discussed in the previous experiment. For this reaction, the rate law takes the form rate = k [I - ] m [BrO 3 - ] n [H + ] p ( 2 ) One of the main purposes of the experiment will be to evaluate the rate constant, k, and the reaction orders m, n and p for this reaction. We will also investigate the manner in which the reaction rate depends on temperature and will evaluate the activation energy, E a , for the reaction. Our method for measuring the rate of the reaction involves what is frequently called a "clock" reaction. In addition to Reaction 1, whose kinetics we will study, the following reaction will also be made to occur simultaneously in the reaction flask: I 2 (aq) + 2 S 2 O 3 2- (aq) 2 I - (aq) + S 4 O 6 2- (aq) As compared with (1) this reaction is essentially instantaneous. The I 2 produced in (1) reacts completely with the thiosulfate, S 2 O 3 2- , ion present in the solution so that once all the thiosulfate ion has reacted, the concentration of I 2 is effectively zero. As soon as the S 2 O 3 2- is gone from the system, the I 2 produced by (1) remains in the solution, and its concentration begins to increase. The presence of I 2 is made strikingly apparent by a starch indicator which is added to the reaction mixture, since I 2 even in small concentrations reacts with starch solution to produce a blue color. By carrying out Reaction 1 in the presence of S 2 O 3 2- and a starch indicator, we introduce a "clock" into the system. Our clock tells us when a given amount of BrO 3 - ion has reacted (1/6 mole BrO 3 - per mole S 2 O 3 2- ), which is just what we need to know since the rate of reaction can be expressed in terms of the time it takes for a particular amount of BrO 3 - to be used up. In all our reactions, the amount of reactants that react in the time
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Iodine Clock Reaction Experiment Five Chemistry M01B Laboratory Manual pp. 23 we measure will be constant and small as compared to the initial amounts of those reactants. This means that the concentrations of all reactants will be essentially constant in Equation 2, and hence so will the rate during each reaction. In our experiment, we will carry out the reaction between BrO
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This note was uploaded on 03/30/2010 for the course CHM chemisty l taught by Professor ? during the Spring '10 term at University of North Carolina Wilmington.

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experiment_five - Iodine Clock Reaction Experiment Five...

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