1. a. Calculate the initial rates for Experiments 1, 2, and 3 from ?[S 2 O 8 -2

Question

1.   a. Calculate the initial rates for Experiments 1, 2, and 3 from ?[S2O8-2]/?t. Use mean elapsed times. Give correct units.

                              b. Obtain the reaction orders with respect to the S2O8-2   and I-1   ions. Remember that your results have been influenced by experimental error.

                              c.   What is the correct rate equation?

d.   Calculate the initial concentrations of the S2O8-2   and I-1   ions in Experiments 1, 2 and 3.    

      Remember that dilution occurred when the solutions were prepared.

e.   Calculate the rate constant in Experiments 1, 2, and 3, and obtain the mean. Give the correct units.

Results Laboratory temperature: 30.°C Elapsed Experiment Trial Start End Time(s) 2 1 0 226 220 20. 2131 2:3) 1 0 12 JY2 O :35 125 0 : 23 23 20. ligy 2:24 1 0 0 2300 temp: 32 a + 6 0.040.04 5

Explanation / Answer

1. d) Calculated concn of S2O8-2 and I- :

Concn of S2O8-2 in bottle x Volume taken = Concn of S2O8-2 in solution x Volume of Solution

For Experiment 1,

0.2 x 2 = Concn of S2O8-2 in solution x 11

Concn of S2O8-2 in solution = 0.0363 M

For Experiment 2,

0.2 x 4 =  Concn of S2O8-2 in solution x 11

Concn of S2O8-2 in solution = 0.0727 M

For Experiment 3,

0.2 x 2 = Concn of S2O8-2 in solution x 11

Concn of S2O8-2 in solution = 0.0363 M

Similarly for I-,

Concn I- of  in bottle x Volume taken = Concn of I- in solution x Volume of Solution

For Experiment 1,

0.2 x 2 = Concn of  I-  in solution x 11

Concn of  I-  in solution = 0.0363 M

For Experiment 2,

0.2 x 2 =  Concn of  I-  in solution x 11

Concn of  I-  in solution = 0.0363 M

For Experiment 3,

0.2 x 4 = Concn of  I-  in solution x 11

Concn of  I-  in solution = 0.0727 M

1. a) Initial rates(M/sec)

For Experiment 1, rate= Concn of S2O8-2/avg.time=0.0363/145.5=0.000249 M/sec

For Experiment 2, rate= Concn of S2O8-2/avg.time=0.0727/98.5=0.000738 M/sec

For Experiment 3, rate= Concn of S2O8-2/avg.time=0.0363/83.5=0.000434 M/sec

1. b) Rate = k x [S2O8-2]x x [I-]y

Let the rate for Experiment 1 be R1, then,

R2= 2x x R1 and R3= 2y x R1

From the calculated values in part 1. a),

R2/R1=2.963= 2x So the closest power of 2 makes x=1

R3/R1=1.7429= 2y So the closest power of 2 makes y=1

1. c) The correct rate eqn is Rate = k x [S2O8-2] x [I-]

1. e) Rate = k x [S2O8-2] x [I-] k = Rate/([S2O8-2] x [I-])

For Experiment 1, k= 0.000249 / (0.0363 x 0.0363) = 0.188 M-1sec-1

For Experiment 2, k= 0.000738/ (0.0727 x 0.0363) = 0.027 M-1sec-1

For Experiment 3, k=0.000434 / (0.0363 x 0.0727) = 0.164 M-1sec-1

Mean k = 0.126 M-1sec-1

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