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

Apparatus

Chemicals

Data Collection and Processing

Table Showing The Time Taken for Each Different Type of Solution to React

As the results above show, as the volume (which is used here instead of concentration, but they are equivalent) of the H2O2 is doubled, the rate falls, but not at a constant or perfectly exponential rate. This is probably due to the fact that there were large uncertainties present in the experiment, meaning there will be an error, which is apparent in the results above. The full extent of the errors are evaluated in the evaluation section of this lab report.

 

Calculating Rate

Rate can be determined used the equation   where time is substituted by the tame taken for the reaction to happen in each experiment. 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

Volumes of Reactants and Rate for Experiment 2

Volumes of Reactants and Rate for Experiment 3

Volumes of Reactants and Rate for Experiment 4

Volumes of Reactants and Rate for Experiment 5

Volumes of Reactants and Rate for Experiment 6

Volumes of Reactants and Rate for Experiment 7

Volumes of Reactants and Rate for Experiment 8

Volumes of Reactants and Rate for Experiment 9

The uncertainty of rate was calculated with the equation 1/3.19 x 100 = 31%. 3.19 is the time taken for the quickest reaction, and 1 is the uncertainty. This uncertainty is the greatest of all and is applied to all experiments.

As the graph above demonstrates, the rate becomes proportionally slower as the volume of H2O2 is increased, showing that it is most likely 1st order. When increasing volumes of Ethanoic Acid are added, the rate remains about the same, showing that it is most likely 0 order.

The full rate equation cannot determined since the chemicals in solution A were not tested for their order.

Conclusion

From this experiment I can conclude that the order of H2O2 is 1st order and that Ethanoic Acid (CH3COOH)  is 0 order. This is because as the volume of H2O2 increased by a factor of two, the rate increased at a constant rate. Since first order states that as concentration increases, the rate increases by the same factor. This is exhibited with H2O2, as volume increases by 2, rate increases from 0.05 to 0.1. The rate does not increase by exactly two due to the variables and errors in the experiment. The rate remains constant when the concentration of the ethanoic acid increases, meaning it is 0 order. The reason the rate is not completely constant is due to the errors and variables. The uncertainty of the rate was ±31%, which is somewhat significant. The uncertainty of the measuring cylinder was ±0.5ml, so the greatest uncertainty (using the 2ml samples since the uncertainties for these were the most significant) was 25%. The third uncertainty was the human error of ±1 second. None of these uncertainties are large enough to discount the final results; an improvement on each can be found in the evaluation. Literature values state that H2O2 is first order and ethanoic acid is 0 order, which agrees with the conclusion made in this investigation. Source:

Evaluation 1

There are several areas of weakness in the investigation which are evaluated below:

Evaluation 2

Bellow are methods outlining the ways the error can be eliminated or reduced.