Iodine Clock Abstract

416 Words2 Pages
The purpose of this experiment was to determine the effects of concentration, temperature and a catalyst on the rate of the iodine-hydrogen peroxide reaction and to also determine the rate law expression for the reaction. Mixture #1 which was made up of 10ml of KI, 15ml of Buffer, 5ml of Na2S2O3 and 15ml of H2O was prepared in an Erlenmeyer flask and three drops of 3% starch (indicator) was added and the mix was stirred carefully. The temperature (19.70C), pH (4.78) of the mix was carefully obtained. An accurate measurement of 5ml of H2O2 was then added to the mix and the mix turned from a clear solution to a blue solution and then finally black. The reaction time (156.5s) (i.e time taken from solution to turn from clear to blue) of the mix was carefully obtained. The same process was applied to mix #2, #3 and #4 but with different volumes of compounds and the temperature, pH and reaction time was also carefully noted. For mixture #5, the composition from previous mixtures remained the same but 5ml of Mo(VI), a catalyst, was added. The temperature was duly noted and the reaction time (54.5s) was also recorded. For mixture #6, the composition also remained the same but the temperature of the mixture was lowered to 100C and the reaction time (309s) was noted. I realized that that in the presence of a catalyst, the reaction occurred at a faster rate and when the temperature was decreased, the reaction rate was doubled. The concentration of the ions in the compounds was also calculated for every mixture with the dilution formula (C1V1=C2V2) and the reaction rate was also calculated by comparing a ratio of the concentration of blue starch complex (S2032-) and reaction time. The rate constant was also calculated for mixtures #1 - #4. The order of the different reactions was calculated by substituting known values for rate and concentration into the rate law giving rise to
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