Chemical Reaction End Point Timer. - page 5
Keywords: Physics Chemistry Practical Build device end point timer
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 5 of 9 pages: 1 2 3 4 5 6 7 8 9
67 seconds
Although my voltmeter gave readings to 3 decimal places I have only used 2 decimal places in my results as the last digit of the voltmeter was constantly changing up and down due to the random error caused by movement in the room. The box that I built around my apparatus successfully reduced this to the 3rd decimal place as before it was much larger. I also took 3 repeat readings for each set of results so that any human error would show up. So, I can be fairly confident that my results are accurate.
Analysis
My first preliminary experiment was just to get a rough idea of reaction time and doesn’t have much bearing on my results. The next two were rough practices and this is reflected in the results, some values are missing for the first one and the graph is bumpy indicating erroneous results, the second graph is smoother showing that my accuracy has progressed.
The graphs for all my results show the same basic curve shape, the graph starts out flat then begins to slope downwards at first gently then more steeply before flattening out again. The gradient of the graph corresponds to the speed of the reaction and so this tells us how the reactions went, at first not much happening then picking up speed with the main part of the reaction happening in a relatively small amount of time and then tailing off. It also explains why it is difficult to get a value for the end point when judging by eye as there is no definite end point, the reaction just slowly tails off. It is quite difficult to say exactly when the end point is and would be virtually impossible without the graph, in fact it is the last value before the graph becomes completely flat, but as the curve there is very shallow the actual difference in opacity that you would observe would be almost non-existent. This explains why my judging by eye values were often a long way before the end of the curve. For example when looking at the graph for the 2M experiment you can say that the end point is approximately 255 seconds but when judging the end point by eye I got 67 seconds, in fact at this point the curve is still in its steep section although it is tapering off slightly. This is interesting as it
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