The temperature of the acid - Sample Essay
A graph showing temperature against time taken to collect 50cmi?? of carbon dioxide gas when 50cmi?? of Hydrochloric acid is added to two indigestion tablets As this graph and these tables show, all my results are very close together, and on my graph, the average is barely distinguishable from the other two lines. Therefore, when plotting a graph of rate against temperature, I shall use the average result. I will do this by using the equation Rate equals: A change in something (eg. loss of mass/mass of gas given off) Divided by The time it takes to change/disappear(see page 1).
Therefore, here, rate equals 50 divided by the average time it took to give off 50cmi?? gas (in seconds). For example, at 10i?? C I would do: 50 = 1. 1 (to one decimal place) 44 A table showing the rate of the reactions at the different temperatures Temperature (i?? C) Average (secs) Rate A graph showing temperature against rate of reaction while collecting 50cmi?? of carbon dioxide gas when 50cmi??of Hydrochloric acid is added to two indigestion tablets Analysis of my results My results when plotted on a graph, and the best-fit line accompanying them, show a strong positive trend, as I had predicted.
They do not fall along a straight line, but I didn’t expect them to do so (see original graph, page 2). They do not strictly follow the pattern I originally expected them to do (start off accelerating slowly, then speed up), indeed, they start off accelerating slowly, speed up, slow down, speed up again and then slow back down. Conclusion.
My conclusion fully supports my previous hypothesis and predictions that ‘as the temperature increases, the calculated rate of reaction increases. ‘ This is shown in my final table of results and graph. However, it does not support my predicted results exactly, as the pattern of the graph is not as I had expected. This can be explained if necessary by inaccuracy of equipment, error in timing or simply human reaction times and judgement and therefore is less important than the accuracy of the predicted fact that the temperature and the rate of reaction are proportional.
From my earlier notes I can see that this is because as the temperature increases there is more heat energy. This can be converted into kinetic energy, which makes the particles move around faster, and therefore have more chance of colliding with each other. Also, larger volumes of heat and energy means more effective collisions are created. I therefore conclude that the relationship between temperature and rate of reaction is indirectly proportional, in that as the temperature increases, the rate of the reactions taking place increases also. Evaluation.
I feel that both my method and equipment were fairly reliable, as my results fit fairly closely with how I imagined they would. I have taken enough results and repeats, and these are close enough to my prediction to create and support a firm conclusion. However, a few of my results were slightly anomalous, and the graph did not end up in the exact shape I had predicted, and therefore there must be ways to make my experiment more accurate. There are several things I have noticed which could have adversely affected any results I got, and I have tried to think of ways in which I could alter them if I was to re-do the experiments now.
It is important to remember that the line of best fit on my graph is a straight line, showing only a basic upward trend, not a graph which accelerates as I predicted. When, towards the end of the given time for practicals, I was looking to re-do any points, I only looked at my first graph of time taken against temperature (see page 10), not at the graph of rate against temperature. Therefore, instead of trying to repeat points which fall a little away from my best-fit line, such as that at 24i?? C or that at 50i??C, I added another point at an important stage in my original graph, at 18i?? C.
This seemed a valuable point, but looking at my rate graph it lies exactly on my best-fit line. So while it does serve to highlight the accuracy of my results and best-fit line, it would probably have been more valuable to repeat the points at 24 and 50i?? C. Because of reasons stated (on page 8), the point at 50i?? C didn’t have a repeat to begin with, and therefore ought to be looked at as less valid than the other points anyway.
Most of the potential inaccuracies in my experiment were caused by my equipment, rather than the method, as I felt that my method was reliable. I especially liked my system for heating, as it almost invariably kept the acid and tablets at a constant temperature and it produced accurate results. There are a few reasons that I can identify why the rate may have been above my best-fit line (such as at 24i?? C). If this is the case, it means that the product of 50cmi?? carbon dioxide was produced within a shorter time than expected.
This could be due to the temperature being higher than I had believed (for example if it rose during the reaction), or the gas syringe not being back to exactly zero before starting the experiment (sometimes I found it got knocked so it was already at approximately one or two cmi?? ). Therefore, in theory, checking and making sure of both these things before the start of each experiment could have improved my method, and if I was to repeat the experiment I would ensure I was doing these things. There are also reasons why the rate may have been below my best-fit line (such as at 50i??C).
This means that the product (50cmi?? of carbon dioxide) took a longer time to be produced than expected, or that it took a longer time than average to show in the gas syringe. This could be due to the temperature being lower than I thought (for example having dropped during the reaction). In future, this should be checked before the experiment is started. It could also be due to faulty equipment, like the gas syringe getting stuck or the rubber joining the tube not being on properly, or being on different amounts so that the gas took longer to travel up the tube.
If the experiment was repeated, the gas syringe should be chosen carefully as one which is not either too loose or too stiff, and the joining tube should be put on properly, so that no gas is allowed to escape when the pressure builds up inside the conical flask. Also, a certain degree of error must be allowed for in that a second person is necessary when starting an experiment. This is because you need one hand to add the tablets, one hand to put the bung in and a third hand to start the stopclock. This increases the chances of the experiment being inaccurate, as two different people are very unlikely to be completely synchronised.
Therefore the gas has time to escape unnoticed at the start of each reaction before the bung is put in. I can see little which could be done about this in future experiments. In both cases (above or below the best-fit line) the experiment would have benefited from a greater number of results being taken at smaller intervals. This would probably have further supported my conclusion and may also have more accurately displayed a less obvious trend such as the one I originally predicted.
Taking results in a wider range, (for example from 5i?? C to 70i??C) with repeats to verify accuracy, would have strengthened my evidence. It would only have done this if, as I imagine, a continuing trend showed in the extra results. In all of the experiments, a degree of error in continuity must be taken into account. It is extremely unlikely that the tablets all had the same mass, or that there was the same volume of hydrochloric acid down to the last drop. I tried to make this as accurate as possible, using a burette instead of a measuring cylinder, and only getting the tablets out at the last minute so that they were as whole and un-tampered-with as they could be.
If the experiment was to be repeated on a larger timescale, I could measure the mass of the tablets to increase accuracy. It is also impossible to swirl the beaker at exactly the same vigorousness every time, although I tried to keep it as constant as I could. If I was looking to test these results on a much wider scale, I could use other common antacid tablets with similar active ingredients, keeping the type and volume of acid constant. This would prove that the tablets that I used were regular, and didn’t just coincidentally produce typical results.