5 mls of water, 10 mls of HCl and 10 mls of water, 7. 5 mls of HCl and 12. 5 mls of water, 5mls of HCl and 15 mls of water, 2. 5 mls of HCl and 17. 5 of water. We then repeated all these results 5 times so that we could take an average and give us a more correct result. I think we need at least this many to give us a fair average- otherwise it might be biased by anomalous points. We then put all the results into tables, took averages and drew graphs. Safety: Where any of the results went straight up to 100 cm cubed, after 5 seconds we removed the bung from the test tube.
If much longer had been left, this could have been dangerous due to a build up of pressure resulting in the shattering of the test tube. Prediction The experiment we will do will involve the concentration of 2M HCl when it is added to powdered marble. I predict that the lower the concentration of HCl the less gas will be produced in the 60 seconds we will be timing for. I think this will happen because water does not react with marble, so the less HCl there is in the conical flask, the smaller the reaction and so less gas will be produced.
Obtaining Evidence The most important thing in the whole experiment is that we performed it in a safe way. For this reason, we wore safety goggles throughout and we used the HCl cautiously to make sure that we didn’t spill anything. We both made sure that we knew that if we did spill any on ourselves or anything else, we would halt the experiment immediately and wash our hands thoroughly and wipe up any HCl that might have been spilt. When we perform the experiment, we will take 5 sets of results so that we can take an average from them.
This will give us a more likely set of results and we will then be able to say what we found out. If we only took one set of results, we might have anomalous points and not realise it. This would give us an unfair set of results and therefore the wrong conclusion. One of us wrote the results down in clear tables so that only one pair of hands was wasted, and the other took control of most of the experiment. To get as accurate results as we could, we had to make sure that we performed the experiment carefully.
This meant we had to keep all the factors that might affect the experiment the same every time. We also had to make sure that nothing else affected the experiment. This meant that we had to wash out the conical flask every time we performed the experiment. We also made sure that we read the results off the gas syringe as close to exactly ten seconds between readings, and we used a stop watch to keep the time. We made sure all the gas from the syringe was expelled before repeating the experiment. We took amounts of HCl from a burette very carefully so as not to go over or under the specified amount.
The results we took were spread over a god range, from 2. 5 mls of acid in the solution to 20 mls in the solution. Results too close together would not give a very obvious conclusion. We repeated the experiment several times in case our results varied a lot. We then worked out the averages and plotted them on a graph. Analysing evidence and drawing Conclusions We have found out: We have discovered that the higher the concentration of HCl, the more gas (oxygen) is produced when it is reacted with marble chips. Processing Results
I processed my results by making tables for all the results. From these, I calculated averages for each concentration of acid, and made another table to show these. I then made a graph showing all the averages. From this graph, I could that a pattern had developed. It showed that the lower the concentration of acid, the less gas was produced. I also calculated the gradients of each line on the graph. 0. 25M. 13 divided by 10 = 1. 3 0. 5M. 15 divided by 2 = 7. 5 0. 75M. 11 divided by 1 = 11 1M. 15 divided by 3 = 5 1. 5M. 10 divided by 1 = 10 1. 75M. 13 divided by 1 = 13
This generally showed that the higher the concentration of the acid, the higher the gradient of the graph. The Collision Theory When a reaction takes place, the particles of the reacting substances must collide with each other and the activation energy must be reached for the reaction to occur. The reaction will be speeded up if the number of collisions is increased. This can be done by increasing the temperature, by which the particles gain more energy and so the reeaction happens quicker, and also by changing other variables, of which can be read about in my planning section.
However, the variable I am interested in is concentration, and if a solution is more concentrated this will result in more particles of the reactant hitting about between water molecules, which creates collisions between important molecules more likely. If a solution is more dilute, there are less important molecules for th reactant to collide with and so the rate of reaction is slower. Conclusion- prediction proved? My prediction was proved right. This was shown by our results, which showed that the lower the concentration in a set amount of HCl, the less gas was produced when it was added to marble chips.
We did expect this as we knew there was less acid in the set amount of 20 mls as it was diluted. This meant there was less acid for the marble chips to react with, and thus less gas was produced. We realised this might happen because of similar experiments that we have done in the past which show us that the more diluted things are, the less strongly they react. Evaluation I think our experiment worked quite well but there was definitely room for improvement. I think that a couple of our results were inaccurate because my graph and tables show the 1.
5M acid managed to produce more acid than the 1. 75M acid, when it should have produced less. I think this is because we did not get the bung into the flask quick enough and this made a significant difference to the results. We also had an old syringe and this could have meant that it got stuck at one point and we had to free it, which would have made a small difference to our results but I think that this is unlikely because I have no recording of it and I do not remember it happening either. We also would have performed the experiment again if this had happened.
However the reason may have been because of a slight fluctuation in the temperature of the room. I think this or the reason that we didn’t get the bung in quick enough are the most likely reasons because we wouldn’t have noticed anything odd happening. We could have prevented the temperature from fluctuating by perhaps performing all the experiments in a water bath, keeping the temperature at a constant, for example 30 degrees. It was probably not the best method to carry out the experiment but it was the best we came up with with the equipment we had.
If we had had more advanced apparatus, perhaps we would have had a better system so that no gas escaped and the results were precise rather than the “close” ones we got. If I did the experiment again, I would like a better system of preventing any gas from escaping so that the results were more accurate and it was a fairer test. We could have used something that had a separate container inside it which we could have put the marble chips in and the HCl in the main container. Then we could have tipped the small container inside the large one to release the chips. No gas could have escaped.
We also could have done more experiments between the ones we performed, at say 0. 3M, 0. 4M etc. This would have made our results more reliable and would have backed up our result with more evidence. I could have drawn my graph on the computer which would have made it more accurate, but the facilities for drwing line graphs mean that the line follows the points exactly and does not allow for anomolous results and so does not give a smooth curve. This would not have allowed me to draw a reliable graph or find the gradient of the lines, which meant that although it was not a great option, I had to do it by hand.
I think we had enough results to draw a sensible conclusion because we still managed to get clear results to prove our prediction right even though we did have a couple of anomalous results. However we only had one slight anomolus result, on the 0. 5M line on the graph, and the fact that the tables showed that the 1. 5M acid produced more gas than the 0. 75M acid, which shows that although our capabilities were limited, we managed to prove our prediction, even if it was not as accurate as we would have liked.