Key Prob Set 3 09-106 S 11

# Key Prob Set 3 09-106 S 11 - Name Recitation(CIRCLE ONE TA...

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1 Name ______________________________ _ 09-106 Spring 2011 Recitation ( CIRCLE ONE TA and ONE TIME ): Christian Steve Brendan 6:30 7:30 Problem Set 3 DUE Wed. 2/23 IN LECTURE (20 points) 1. In a “clock” reaction, a dramatic color change occurs at a time determined by concentration and temperature. One of the most famous is the iodine clock reaction. The overall reaction is: 2 I - (aq) + S 2 O 8 2- (aq) b I 2 (aq) + 2 SO 4 2- (aq) rate = k [I - ] x [S 2 O 8 2- ] y As I 2 forms, it is immediately consumed by its reaction with a fixed amount of added S 2 O 3 2- : I 2 (aq) + 2 S 2 O 3 2- (aq) b 2 I - (aq) + S 4 O 6 2- (aq) ( a side reaction ) s Once the S 2 O 3 2- is consumed , the excess I 2 forms a blue-black product with starch solution present in the mixture: I 2 + starch b starch-I 2 (blue-black) ( another side reaction ). The time it takes for the blue-black color to appear is thus when the reaction is over, and thus it is recorded. The following data were measured for an iodine clock reaction at 298 K:

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Key Prob Set 3 09-106 S 11 - Name Recitation(CIRCLE ONE TA...

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