Iodine Clock Rxn Lab

Purpose: To determine the general rate law for the reaction of S2O82- + I- through a series of experiments and calculations.

Materials:
-Temperature probe
-3 large test tubes
-3 rubber stoppers
-Pipets
-0.20 M KI soln
-0.20 M NaCl soln
-0.010 M Na2S2O3 soln
-2% starch soln
-0.20 M K2SO4
-0.20 M K2S2O8
-0.2 M CuSO4
-Timer or stopwatch
-Small beaker
-Hot water

Procedure: Refer to Lab #12, No changes

Data:
Table #1: Quantitative/Qualitative Observations Room Temp: 25.4°C Experiment | Time | Temperature | Observations | 1 | 1 min, 57.76 secs | 25.4°C | Turned dark purple after a while wait | 2 | 1 min, 1.88 secs | 25.4°C | Very quickly turned dark purple | 3 | 59.95 secs | 25.4°C | Most rapid rxn, turned dark purple quickly | 4 | 1 min, 10.13 secs | 35°C | Alarmed that rxn was not very fast | 5 | 2.38 secs | 24.2°C | When catalyst added, rxn completed immediately |

Calculations: 1) M1V1 = M2V2
K2S2O8
Experiment 1
(0.20M)(2.0mL) = M2(11mL)
M2 = 0.036 M

Experiment2
(0.20M)(4.0mL) = M2(11mL)
M2 = 0.073 M

Experiment 3
(0.20M)(2.0mL) = M2(11mL)
M2 = 0.036 M

I-
Experiment 1
(0.20M)(2.0mL) = M2(11mL)
M2 = 0.036 M

Experiment 2
(0.20M)(2.0mL) = M2(11mL)
M2 = 0.036 M

Experiment 3
(0.20M)(4.0mL) = M2(11mL)
M2 = 0.073M

2) Rate = ½ ([S2O33-]/Δt)i
M1V1 = M2V2
(0.010M)(2.0mL) = M2(11mL)
M2 = 0.0018 M (For experiment 1, 2, 3)
Experiment 1
Rate = ½ [0.0018M]/(117.76secs) = 7.7 x 10-6 M/s
Experiment 2
Rate = ½ [0.0018M]/(60.88secs) = 1.5 x 10-5 M/s
Experiment 3
Rate = ½ [0.0018M]/(59.95secs) = 1.5 x 10-5 M/s

3) Table of Experiments 1, 2, 3

Experiment | Initial [S2O82-] (M)Rxn Order = 1st | Initial [I-] (M)Rxn Order = 1st | Initial Rate (M/s) | 1 | 0.036 | 0.036 | 7.7 x 10-6 | 2 | 0.073 | 0.036 | 1.5 x 10-5 | 3 | 0.036 | 0.073 | 1.5 x 10-5 |

Exp. 1 2
[S2O82-] x 2
[I-] constant S2O82- first order
Rate x 2

Exp. 1 3
[S2O82-] constant
[I-] x2 I- first order