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Aim: Using an iodine clock reaction to find the order of hydrogen peroxide and Ethanoic acid present in that experiment.

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Introduction

Design Aim: Using an iodine clock reaction to find the order of hydrogen peroxide and Ethanoic acid present in that experiment. Relevant Chemicals Equations Below are the two steps of the reaction. The reactants in red are the reactants whose volumes were changed, and are the reactants that made up solution B. The other reactants in both equations are the substances which make up solution A. H2O2(aq) + 3 I-(aq) + 2 H+ = I3- + 2 H2O Slow I3-(aq) + 2 S2O32-(aq) = 3 I-(aq) + S4O62- Fast In the equations above, the hydrogen peroxide and H+ ion (from CH3COOH) causes the iodine ions to combine into an I3 molecule. The iodine does not immediately react with the starch since it is paired with potassium, (which in this case is a spectator). The slow reaction produces I3-, which then reacts with sodium thiosulphate to produce individual I- ions, which then bind with the starch, causing the dark blue - black coloring of the solution. Variables Variable Type of Variable How to Control / Manipulate / Measure Volume of H2O2 and Ethanoic Acid Independent In 5 sets of experiments, the H2O2 was changed and the Ethanoic acid held constant among others (look below) ...read more.

Middle

For example, to calculate the rate in the first experiment, where H2O2 has a volume of 2ml, the acid has a volume of 10ml and the water has a volume of 8ml and the time taken is 22.15, the equation would be , which equals cm3/s. This can be used for the other experiment, the results are shown in the table below. Volumes of Reactants and Rate for Experiment 1 Volume of H2O2 ml, �0.5 Volume of CH3COOH ml, �0.5 Volume of Water ml, �0.5 Rate , cm3/s �31% 2 10 8 0.045 Volumes of Reactants and Rate for Experiment 2 Volume of H2O2 ml, �0.5 Volume of CH3COOH ml, �0.5 Volume of Water ml, �0.5 Rate , cm3/s �31% 4 10 6 0.104 Volumes of Reactants and Rate for Experiment 3 Volume of H2O2 ml, �0.5 Volume of CH3COOH ml, �0.5 Volume of Water ml, �0.5 Rate , cm3/s �31% 6 10 4 0.160 Volumes of Reactants and Rate for Experiment 4 Volume of H2O2 ml, �0.5 Volume of CH3COOH ml, �0.5 Volume of Water ml, �0.5 Rate , cm3/s �31% 8 10 2 0.220 Volumes of Reactants and Rate for Experiment 5 Volume of H2O2 ml, �0.5 Volume of CH3COOH ml, ...read more.

Conclusion

If one were to determine the order of the reactants in solution A (starch, potassium iodide and sodium thiosulphate), more experiments would have to be carried out to determine the order of each; I would advise 5 experiments per reactant. Evaluation 2 Bellow are methods outlining the ways the error can be eliminated or reduced. Error How to Eliminate/Minimize Uncertainties There were several uncertainties present in the investigation. There was a total uncertainty of �31% on the rate, a maximum of 25% uncertainty on each measured solution, giving a total uncertainty of 100% per experiment since four solutions were measured. A dropping pipette could have been used in order to minimize the uncertainty. Timer Error The uncertainty derives from the failure to start and stop the timer at the appropriate times. The uncertainty was �1 second, which is not significant enough to have detrimental effects on the final result. This can be minimized by using a more precise timer which would start precisely when the solution reached 40ml and stopped when the reaction had finished. Data Set Limitations More trials with a larger range of concentrations would have provided a larger range of results and a more definite conclusion could have been made. A suggestion would be 10 changes in concentrations for each reactant. ?? ?? ?? ?? ...read more.

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