Chemical Reaction End Point Timer. - page 6
Keywords: Physics Chemistry Practical Build device end point timer
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 6 of 9 pages: 1 2 3 4 5 6 7 8 9
tells me that the results from all the experiments I have done which used the judging by eye technique are likely to be quite inaccurate.
The end points for all the curves are actually fairly similar, if you look closely the line becomes flat at some point between 250 and 300 seconds. This is again quite different to my judging by eye values which decrease as the molarity increases, they do bear some relation to the area where the curve begins to flatten out though which does happen earlier as the molarity increases. The basic shape of all the curves stays the same, however when the molarity is changed some things do alter slightly.
The main changes are: the gradient of the graph in its steepest stage, how gradually the gradient changes between the steep and the flat sections and how far the graph drops before it finally flattens out. All the curves start at the same value of volts – approximately 5.5V.
The graph for 0.5M only drops by about 2V and even at its steepest the gradient is fairly low, also the gradient changes quite gradually; for 1M the graph is steeper during its main section and the gradient changes more suddenly and less smoothly than 0.5’s, the graph also drops further, over 3V; for 1.5M the graph is actually less steep than 1’s, its gradient changes more gradually and it drops a little less, not quite 3V, although it is further on in these things than 0.5; for 2M although the steepness of the graph, the rate at which the gradient changes and the amount the curve drops (3V) are all more than 1.5’s they are actually still not quite as much as 1’s.
This is surprising, what you would expect to happen is that as the molarity (and so the rate of reaction) is steadily increased the changes in the graphs would also steadily increase. If you look at the other three graphs excluding 1M this does happen. The curve of the graph becomes more pronounced faster, indicating a faster reaction, and for the higher molarities the graph drops further down the voltage scale showing that the solution for those molarities was more opaque when the reaction finished – more reacting took place. The graph for 1M doesn’t quite fit this pattern it is slightly further along it than it should be - it looks more like you
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