Prediction
I predict that as the concentration of the sodium thiosulphate increases the rate of reaction will increase. This means that one graph drawn up in my analysis will have negative correlation and one will have a positive correlation because they have been drawn with opposite axis, the graphs will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration is increased. This can be justified by relating to the collision theory. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully.
Background Information - Concentration – If the concentration of a solution is increased there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other thus meaning a faster rate of reaction.
Pressure - If the pressure is increased the particles in the gas are pushed closer. This increases the concentration and thus the rate of reaction.
Surface Area – If a solid is powdered then there is a greater surface area available for a reaction, compared to the same mass of unpowdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas.
My Results
Data Analysis
These are the results I had gained from my experiment, these results match my prediction because I predicted that as the concentration increases so will the rate of reaction which means the experiment will finish quicker. This matches my actual results and it shows that I was correct in my prediction, these results fully support my conclusion that the rate of reaction will increase as concentration increases. As you can see the time of the experiment increases as the formula becomes less concentrated and this is because there are less particles colliding with each other which means the rate of reaction will be slower.
If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself. For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area.
I have also researched on the effects of a catalyst to try and explain why this is occurring in the experiment. A catalyst works by providing an alternative reaction pathway that has lower activation energy. A catalyst does not alter the Maxwell-Boltzmann distribution. Because a catalyst provides a reaction route of lower activation energy, however, a greater proportion of particles will have energy greater than the activation energy. This is practically saying that as a solution with a higher concentration is added the rate of reaction will increase just like my results have shown.
To show my results in a different way I will calculate the rate of reaction for each experiment.
Rate= change in a given property/ Time taken for the change to occur
40 Na S O + 10cm HCL= 40/39.58=1.01
30 Na S O + 10cm HCL=30/52.7=0.56
20 Na S 0 + 20cm H 0 + 10cm HCL=20/80.28=0.249
10 Na S O + 30cm HCL=10/212=0.047
As you can see the rate of reaction is clearly dropping as the concentration becomes less, rate is dependant on the number of collisions per second and it is clear that the number of collisions per second is going down as the concentration is going down.
I have also drawn two graphs to show the results of the experiment and how it went. The two graphs I have drawn also fully support my prediction that one will have negative correlation and one positive. For the first graph you can clearly see negative correlation as the concentration of Sodium thiosulphate is increasing this is further more evidence that the concentration increases the rate of reaction in the experiment.
In the second graph you can see that as the Concentration is increasing the graph is showing positive correlation which means the rate of reaction is increasing as the concentration is increasing because the x-axis is measuring the rate of reaction.
In both graphs you can see that both graphs are curved which means that the concentration does not react perfectly with the time because all the points on the graph are not lined up in a straight line. In the graph to show the relationship between the rate of reaction and concentration you can see that the rate of reaction is practically doubling with the concentration and this shows that every 10cm of increase in the concentration means a double in the rate of reaction. Another way to explain the decline in the rate of reaction as concentration is decreased is the addition of water which is not very reactive at all and the addition of more water will mean that there will be less collisions because there are more water particles than Sodium thiosulphate particles in the water so less collisions are more likely.
Evaluation
In this experiment we used a very simple method and I think it worked well. We did gain a couple of anomalous results which have been shown in red on the results table. This is because both of the results are so far apart from each other you don’t know which should be the true result; I think the length of time had affected this result because it was a lot longer than the other times so it was hard to gain a consistent time. Also because it was such a low concentration we may have made a mistake in measuring and one amount of sodium thiosulphate may have been a lot more than the other.
To make this experiment better and more precise I think we could have used a burette to make near perfect measurements of the sodium thiosulphate and hydrochloric acid, this would help to prevent any of the results being too far different from each other. It would also help if all the equipment was sterilised because this would make sure that there would be no foreign substances in our equipment to start a reaction with either the sodium thiosulphate or the hydrochloric acid. By using a light sensor this would also help because we would also be able to pinpoint the exact time when the X would disappear and this would help iron out any questions over the time when the X actually disappears.
I think that the experiment went reasonably well but there were some things we could have improved on. I think we should have drawn a slightly brighter X because at times we were not sure if it was there or not because the X was so thin and pale. I also think we should have dried the equipment every time after we washed them because sometimes there were little bits of water laying on the surface and this could have caused a difference in the times during the experiments. Another criticism of my experiment was sometimes our timing was a bit inaccurate and our work on the stop watch was not as sharp as it should have been. But overall our experiment went reasonably well and I think we have gained a decent set of results that are quite reliable.
I think I can make a concrete conclusion from this experiment which is that as the concentration increases the rate of reaction will also increase. This has been proven by our results and it would be interesting to see what a further increase in concentration would have done to the results but I think it’s safe to say that a further increase would have lead to an increase in the rate of reaction. The method we used wasn’t by any means perfect but I think it gave us the ability to show what we needed to show and using a better method would have just cut down the anomalous results and further justified what our results have shown. If further lengths were taken in using higher concentrations I still think that the results would have still been the same and it would have added to the evidence that has already been given to me. I definitely think my own results are good enough to make a concrete conclusion and I think the experiment went reasonably well.
Nathan Ranamagar 5S 5set3 Chemistry Mr. Tierney
