chem kinetics model_report - Model Lab Write-up Introduction The purpose of this experiment was to determine the rate law for an iodine clock reaction

chem kinetics model_report - Model Lab Write-up...

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Model Lab Write-up Introduction: The purpose of this experiment was to determine the rate law for an iodine clock reaction. The iodine clock reaction possesses a two-step reaction mechanism where, 3I - + S 2 O 8 2- I 3 - + SO 4 2- I 3 - + S 2 O 3 3I - + S 4 O 6 starch + I 3 - starch-I 3 - complex The first step of this reaction is the rate-determining step. The I 3 - produced in the first reaction is an intermediate and is immediately used in the second step of the reaction. The thiosulfate ion in the second step of the reaction is treated as a limiting reagent. Once its concentration is depleted the I 3 - reacts with the starch to form a blue-black complex. It is at this point that the reaction is treated as having been concluded. Because the first step of the reaction mechanism is the rate determining step, the generic rate law for this reaction may be written as: R= k(I - ) m (S 2 O 8 2- ) n where m & n are the reaction orders and k is the rate proportionality constant. This investigation utilized a standard experimental design to determine the effects of varying the concentrations of ammonium persulfate (NH 4 ) 2 S 2 O 8 , and potassium iodide (KI) on the rate of the reaction. The concentrations of the iodide ions ranged from 0.1-0.5M in experiment 1. The concentrations of the persulfate ion similarly varied from 0.1-0.5M in experiment 2. The concentrations of the persulfate and the iodide ions were controlled in experiments 1 and 2, respectively. Because the sodium thiosulfate was the limiting reagent, the concentration of the thiosulfate ions was fixed at 0.005 M throughout the experiment. The time required for the color change to occur (as measured with a SensorNet photometric probe, 0-6000 lux, 1 reading/second) was determined from to the point where the lux vs.time plot
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