- I will pour the water in the conicle flask (which was on top of the cross) and then pour the Sodium Thiosulphate and the acid in at the same time so I can be sure that the reaction starts at that moment. Then I will start the stop clock.
- I will stir it because I think that it will help the reaction move forward quicker.
- I will repeat each amount 3 times so I can get an average. This will help me to see whether my results are reasonable compared to other results that I will have obtained for those particular quantities.
- Each time I will do the experiment, I will wash the flask out so that any remains/products from the previous reaction don’t interfere with the next one.
Fair Testing:-
The concerntration of acid stayed the same because it was not a varying factor. The total volume stayed the same because the sodium thiosulphate and water worked together to equal a certain volume. When the Sodium Thiosulphate went down, the water went up to fill the correct capacity. I also washed the flask after each individual experiment so any products made before didn’t interfere with the next one. The temperature should have stayed the same because we were in the same place in the room throughout the investigation.
Prediction:-
My prediction is that when the Sodium Thiosulphate decreases, the reaction will increase in time because there will be less collisions because the particles wouldn’t have enough activation energy to break up the bonds at great speed. The more particles that there are of the Sodium Thiosulphate in the same volume, the less space they will have to move around in (with the extra kenetic energy that they have obtained) so will therefore lead to more collisions with other particles that are in their way.
(Below are diagrams of the reaction between Sodium Thiosulphate and the hydrochloric acid in the same volume.)
Sodium Thiosulphate Hydrochloric Acid
Preliminary Work:-
I did not do any preliminary work to decide what measurements/amounts to use. My teacher gave us the amounts however I did use the internet to find out the balanced equation so I knew what the reaction would give me at the end and I used my text book: Chemistry for AQA(Heinemann) by Ann and Patrick Fullick to help me back my prediction with solid scientific knowledge.
Obtaining Evidence
Results:-
Eventually, by using my results, I will go on to produce a line graph. This will help me to compare all of my results. The amount of Sodium Thiosulphate (x-axis) against time (y-axis).
Method:-(what actually happened)
- Firstly, I gathered all my equipment that I needed for the experiment. This helped me as I was more organised and also it saved me time during the investigation by not constantly getting up to get things.
- Next, I measure out the distilled water and Sodium Thiosulphate in the 50ml measuring cylinder and the acid in the 10ml cylinder because the amount of acid that I needed to obtain was a lot less. This helped me to be more accurate about the quantity of acid I had to use. Also when I measured out the reactants, I did this at eye level to improve the level of accuracy again.
- I poured the water in the conicle flask (which was on top of the cross) and then poured the Sodium Thiosulphate and the acid in at the same time so I could be sure that the reaction started at that exact moment. Then I began the stop clock.
- I didn’t stir the solution because I didn’t think to do that when I did the first experiment and as I have to do the same thing to each one to make it a fair test, I decided not to stir the others.
- I repeated each amount 3 times in order to get an average. This helped me to see whether my results were reasonable compared to other results that I had obtained for those particular quantities. As it happens, there was one value that stood out from the rest and I could tell this because the other two results for that same experiment were not even close to the third value.
- Each time I did the experiment, I washed the flask out so that any remains/products from the previous reaction didn’t interfere with the next one.
Problems with the Experiment:-
A problem that I had was to decide whether or not the cross had in fact disappeared. It was hard to make a judgement as to whether it had disappeared or that it was just my (bad) eyes. So I determined my results by trying to make a conscious decision about all of them as fairly as possible.
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Analysis
The Graph:-
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After drawing my first graph, I realised that I could not interpret it because I could not see if there was a relationship between them or not. So I decided to draw a second graph that was a 1/Time graph.
The first of the two graphs is in the shape of a curve. It starts high (on the y axis) and then drops considerably and starts to bend into a curve. This graph shows that the time is higher when the amount of Sodium Thiosulphate is much less. This proves that the more Sodium Thiosulphate that is present, the faster the reaction is/will be.
On the second graph, it is more or less in a diagonal line going across the page from left to right. The 1/time graph therefore shows a better representation of the results because it is now in a form (following a trend; in a straight line) that I can use to check and compare with my first graph to be sure that my impressions and conclusion of the first graph were in fact correct. The second graph shows that as the concerntration of Sodium Thiosulphate increases so does the time that it takes for it to produce the certain amount of sulphur that covers the cross.
This therefore proves that my initial prediction was in fact right, that the reaction will become faster as the concentration of Sodium Thiosulphate increases.
Evaluation
I think that most of my results were of a good quality except one which I highlighted in the results table. All the other results were close in terms of the time it took for the cross to disappear but with one of them, it was clear that it didn’t fit with the rest of them so when I came to find an average, I did not include that result.
I do not think that there were any points on my graph that seem to be out of place. Sure there are points that just miss the trend of the line but all in all, I think that all the results look about right.
Reasons for why I might have got that one bad reading could be because of my judgement. As I said before it is hard to tell when the cross has in fact disappeared and throughout the experiment I tried to keep it the same but maybe for that one result I didn’t see it as clearly and therefore put down that I could no longer see it. Another reason for my bad result could be that I did not wash the equipment (the conicle flask, cylinders) properly which meant that there was still sulphur left in it which therefore affected my result.
I thought that my method was reasonable. It was the best way to do it with the equipment that we had to do it with and the time allowed. In my opinion the way that we had to observe the results was not very accurate and I think that shows in my results with the one incorrect time.
I could have improved my method and maybe therefore improved my accuracy with my results by stirring the solution as I had initially planned to do. This may have been a factor in my overall experiment.
If I had to redo the investigation, and if I had more time I would have chosen my own amounts of each reactant to use by doing some preliminary work. I think this may have made me understand the task at hand a little better than someone giving me the amounts and then carrying out the experiment.
I thought that my results were quite fair, especially with the 1/time graph. Some of the points weren’t on the trend line/line of best fit but the majority of them were on it. The others however were still close to the line to indicate that there was in fact a trend that all the points were following.
To extend on the experiment that I have just completed, I would have used a different method of gaining my results for example data logging which uses the computer to work out a more accurate time than merely using my eyes. The computer can therefore be more precise in detecting the amount of sulphur produced that covers the cross than human intervention.
