Experiment 16: Kinetics: The Iodine Clock

Experiment 16: Kinetics: The Iodine Clock
Jane Smith

Purpose:
The objective of this experiment was for students to apply their knowledge of kinetics and rate laws in order to determine the rate of a chemical reactions, activation energy, and frequency factors of those reactions. Specifically, this experiment was performed using a series of solutions with varying concentrations of KI, Na2S2O3, and (NH4)2S2O3 . Students recorded time elapsed to observe physical evidence of a reaction taking place in a solution. The time elapsed during the reaction was recorded during the experiment, while the rate (M/sec), reaction constant, and activation energies were calculated post-lab.

Data: Reaction Rates and Concentrations Run # | [KI] (M) |
The concentrations of KI for runs 1 through 8 were calculated and measured out at 0.075, 0.050, 0.025, 0.075, 0.075, 0.075, 0.075, and 0.075 molarities, respectively. The concentrations of Na2S2O3 were calculated and allotted at 0.00044 M for runs 1 through 7, and 0.00022 for run 8. The concentrations of (NH4)2S2O8 determined and distributed for runs 1,2,3,6,7, and 8 were 0.0190 M, and for runs 4 and 5 the concentrations were 0.012 and 0.0062, respectively. The rate constants for runs performed at 296 K were calculated to be 0.088, 0.101, 0.109, 0.084, 0.069, for runs 1 though 5, respectively, and was 0.083 for run 8. These rate constants calculated of reactions performed at 296 K seem to inversely correlate with the concentration of KI in the dilution. This is most likely due to KI having a greater power in the calculation of the rate constants because of KI’s n value of 2 being higher than the m value of 1 for (NH4)2S2O8 . The runs performed at decreased and increased temperatures, runs 6 and 7, were found to have comparatively much higher and lower rate constants, due to rate constants being a function of temperature. Run 6, performed at a temperature of 309 K had a rate constant of 0.271, which was a considerably higher rate constant than those runs performed at 296 K. In contrast, Run 7 was performed at a decreased temperature of 278 K, and therefore resulted in a comparatively low rate constant value of 0.024. The values for activation energy were fairly similar among reactions that were performed at 296 K, mostly ranging from 130 j/mol k to about 400 j/mol k, however there were some outliers that were most likely due to human error or error in calculation. Runs 6 and 7 however had comparatively different activation energies, due to their differing temperatures. Run 6 had an decreased activation energy at 120 j/mol K, due to it’s reacting at an elevated