Kinetics - CH 142 Experiment III Experiment II1 Chemical...

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CH 142- Experiment III 1 Experiment II 1 Chemical Kinetics Introduction A company that manufacturers dyes has had problems with its newest shade of purple: crystal violet. With the recent ‘70’s craze, they have been marketing crystal violet for use in the tie-dye process, which normally requires that the color be “set” in highly basic washing soda. However, many disgruntled customers have complained that crystal violet loses its color during the tie-dye process. The head of Quality Control attended the premiere of Dracula and noted the tremendous job that the Chemical Investigation Team did with the blood and has contacted you to investigate the dye decolorization dilemma. She suspects that base may be involved in the loss of color and would like CIT’s interpretation of the role of hydroxide in the kinetics of crystal violet decolorization. Because your company is relatively new, the company proposes to give you a system with which they are already familiar to investigate first. If your interpretation of this system agrees with what they already know, then they will have more confidence in your crystal violet studies. Therefore, it is prudent to put your best foot forward during the Week 1 analysis so that they will trust your Week 2 findings. The known reaction of Week 1 is the decomposition of peroxydisulfate, S 2 O 8 2- , in the presence of iodide as follows: S 2 O 8 -2 + 2 I - I 2 + 2 SO 4 -2 (1) The rate of this reaction can be monitored with a spectrophotometer because the product I 2 reacts with excess I - in the solution to form the colored species I 3 - , triiodide. The absorbance due to triiodide increases during the course of the reaction as it is being produced and can be used as a measure of the rate. I 2 + I - I 3 - (2) colored rate of disappearance of S 2 O 8 -2 = rate of appearance of I 2 = rate of appearance of I 3 - = k[S 2 O 8 -2 ] x [I - ] y During Week 2, you will examine the reaction actually of interest to the dye company. In contrast to the peroxydisulfate reaction, it is proposed that crystal violet loses color over time in the presence of base: C + N(CH 3 ) 2 N(CH 3 ) 2 N(CH 3 ) 2 + OH _ C N(CH 3 ) 2 N(CH 3 ) 2 N(CH 3 ) 2 OH PURPLE COLORLESS This reaction can be represented as follows: 1 Adapted from Chemistry The Central Science, Laboratory Experiments , 6 th Edition, by J.H. Nelson and K.C. Kemp, the Colby College CH 142 Laboratory Manual edited by D. W. King, 2000, and Laboratory Inquiry in Chemistry , by R. C. Bauer, J. P. Birk, and D. J. Sawyer.
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CH 142- Experiment II- 2002 2 CV + OH - CVOH colored The kinetics of this reaction can also be monitored with a spectrophotometer by observing the decrease in absorbance of crystal violet, which can be used as a measure of the rate to determine the rate law: rate = [CV] x [OH - ] y (3) Your task is to determine the form of the rate law and the rate constants for both of the reactions described above: the decomposition of peroxydisulfate and the decolorization of crystal violet.
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