During our experiment, it became clear that there were a variety of errors due to procedure that has culminated in anomalous results producing an inaccurate Kc value. There are two main sources of inaccuracies; systematic errors and equipment errors. The main sources of systematic errors were: ( i ) The amount of phenolphthalein added to the solutions ( ii ) The difficulty in judging the exact point of colour change from colourless to pink during the titration.
( iii ) The difference in judging where the bottom of the meniscus is. The systematic errors are non-quantitative; therefore it is impossible to predict the effect of the errors mathematically. But, due to the repetition of the titration, we are increasing the precision of our results, thereby decreasing the event of an error being produced. Therefore the systematic errors have a relatively insignificant role in our errors. The experimental errors were a result of the inaccuracies from the equipment: ( i ) The burette has an inaccuracy of +/-0.05cm3, thus resulting in a cumulative error of 0.1cm3 and the pipette had an error of +/- 0.1cm3.
( ii ) Minor inaccuracy from the 100cm3 standardizing flask. As the results of the experimental errors produced quantitative errors, it is possible to work out the results in account with the percentage of errors due to the equipment. The calculation has been shown on the analysis sheet. The error due to the burette was (0.05/16.8) x 100 = 0.3%, and the error due to the pipette was (0.1/1) x 100 = 10%. Therefore, the total error due to equipment was 10.3%, ignoring the inaccuracy due to the standardizing flask as it is so small it can be ignored.
Another large source have error cannot have been foreseen. We based our experiment on the fact that the solutions we were given were in equilibrium, but we cannot be sure that this is true. Although the solution were left for a week, to make sure that our solutions were in equilibrium, we could leave the solution for a longer period of time to improve the likeliness of an equilibrium being maintained.
As my results can prove, the precision was very good as my results were close together, but my value of Kc was almost 30% of the data book value of 4.0 for this reaction. As a class, all the solutions should have produced the same Kc value, therefore having the class averages for all the solutions can allow me to analyse the accuracy of my results in comparison to the other experiments:
Kc Averages for experiment: 1. 3.49 no units 2. 1.28 no units 3. 4.11 no units 4. 2.55 no units The overall average for the Kc is ( 3.49 + 1.28 + 4.11 + 2.55 ) / 4 = 2.86 no units. Therefore, as my result for the Kc was 2.82 (no units), with respect to the class, my results were very accurate. Unfortunately with respect to the actual data book value of 4, my experimental error was off by 30% resulting in a fairly inaccurate real result.