Experiment 10 - EXPERIMENT 10 Chemical Kinetics Iodine Clock Reaction Objective The complete concentration and temperature dependence of the

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EXPERIMENT 10 Chemical Kinetics: Iodine Clock Reaction Objective: The complete concentration and temperature dependence of the reaction rate for the reaction between peroxydisulfate ion and iodide ion in aqueous solution will be determined. Introduction: Peroxydisulfate ion reacts with iodide ion in aqueous solution to give iodine and sulfate ion: 2 I - + S 2 O 8 2- → I 2 + 2 SO 4 2- (1) In this experiment you will determine the rate at which reaction (1) occurs. This rate can be expressed in the form of a rate law, Rate = k I " [ ] x S 2 O 8 2 " [ ] y where x and y are the orders of reaction in iodide and peroxydisulfate ions, respectively, and k is the specific rate constant; the specific rate constant is a function of temperature. The initial rate of this reaction will be determined by measuring the time required to generate a certain amount of iodine, the same amount in every trial, according to reaction (1). Two other reactions will be used to signal when this constant amount of iodine has been produced. The first of these two reactions involves thiosulfate ion, S 2 O 3 2- , a certain, identical amount of which will be added to the reaction mixture in each trial. Thiosulfate reacts with iodine as fast as iodine is produced, converting it back to iodide ion: 2 S 2 O 3 2- + I 2 → S 4 O 6 2- + 2 I - (2) Because reaction (2) is so fast, relative to reaction (1), iodine will not have a chance to build up in solution until all of the thiosulfate has been consumed. Any buildup of iodine in the solution indicates that the thiosulfate has been used up, and that, of course, means that the constant amount of iodine has been produced. To visually detect the presence of excess iodine in the solution you will add some starch to one of the solutions before mixing the iodide and peroxydisulfate. As soon as iodine begins to build up in solution it will react to form a dark-blue complex with starch: I 2 + starch → I 2 -starch complex (3) The time period as measured from the time of mixing the peroxydisulfate with the iodide in the presence of starch and thiosulfate to the appearance of the dark-blue color is the time it
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Experiment 10: Chemical Kinetics: Iodine Clock Reaction 10-2 takes to produce a certain constant amount of iodine. The initial rate is inversely proportional to the time period; the faster the rate, the shorter the time period. You will carry out a series of experiments to determine the orders of reaction in iodide and peroxydisulfate ions. In each experiment you will double the concentration of either iodide ion or peroxoydisulfate ion. If doubling the concentration of one reactant while holding the concentration of the other constant (a) has no effect on the reaction rate, the order of reaction in that reactant is zero; (b) doubles the initial rate, the order of reaction in that reactant is 1; or (c) quadruples the initial rate, the order of reaction in that reactant is 2. By measuring the reaction rate at two temperatures you will also be able to measure the
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This note was uploaded on 06/10/2011 for the course CHEM 2090 taught by Professor Zax,d during the Spring '07 term at Cornell University (Engineering School).

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Experiment 10 - EXPERIMENT 10 Chemical Kinetics Iodine Clock Reaction Objective The complete concentration and temperature dependence of the

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