Prediction
I think that when the concentration of the Na2S2O3 is increased, the rate of reaction will be higher. This is because if there are more molecules, they are more likely to collide and react. However, the collision theory says that a very small percentage of these collisions result in a reaction. This is because of an energy barrier. Only particles with enough energy to break the energy barrier will react when they collide. Therefore if the amount of collisions is increased, the rate of reaction will increase but the percentage of collisions will remain the same. The particles go through random collisions in which energy is transferred between the colliding particles and this leads to particles with differing energies. I also think that when the temperature is increased it will have the same effect. This is because the molecules will collide more often and with greater energy and so will be more likely to react because their bonds break. Therefore I predict that in the experiment were the temperature is changed, the rate of reaction will go up as the temperature goes up. In the experiment where the concentration of the thiosulphate is to be varied, I expect also the rate of reaction to go up as the concentration goes up. If the concentration doubles, I would expect the rate of reaction to double and if the concentration is zero I would expect the rate of reaction to be zero.
In the first half of the experiment everything will be kept the same except the temperature, which will range from 10oC to 60oC. The concentration of the sodium thiosulphate used throughout will be 30g/dm. In the other half to the experiment everything will be the same apart from the concentration of the sodium thiosulphate. The concentration will be no less than 15g/dm because any less than this would probably take too long. The hydrochloric acid and the sodium thiosulphate will not be heated and the tests will be done at room temperature, usually around 20oC.
The experiment will be done three times and the results will be made fair by the fact that only one thing will change each time. 5ml of HCl and 20ml of Na2S2O3 will be used.
Results 1
Results 2
Analysis
All results have now been recorded, showing correlation. a repeat was done for each test and an average worked out from the two readings. The results were recorded with a decimal place and the averages and rate of reactions are to two decimal places. The rate of reaction is the key thing being looked at in this experiment and this is how I calculated it:
1
Time taken for cross to disappear
My predictions where correct. When the concentration of the sodium thiosulphate has gone up, the rate of reaction goes up. When the temperature goes up, so does the rate of reaction. This is what was expected and therefore makes it unlikely that there were any major mistakes, although all results are not perfect.
The next pages are graphs. Graphs one and two relate to the first table of results and graph three and four relates to the second table. The reason there are two graphs for the first table is that one shows time taken for cross to disappear and the other shows rate of reaction. The third shows the time taken for the cross to disappear in the second experiment and the fourth shows the rate of reaction in the second experiment. Graph one and three show negative correlations while graph two and four show positive correlation.
Evaluating evidence
The way I used to do the experiments was good and produced good results but it could have been improved. The results are good, there are no odd results and itcame out as predicted. This could mean that the experiment was done perfectly. Although all the average times and rates of reaction all correlate, they are not all evenly spaced and therefore are probably not perfect.
Improvements
It would have been good to do more repeats. Three tests were managed each time but if one had been wrong this could have severely changed the average time and therefore rate of reaction.
Conclusion
I think this was a good experiment and was done as well and as accurately as I could have made it. The results support my predictions and they seem to be reliable.
