2 Method and prediction
4 Results for temperature and concentration on Tables
5 Graph for results for rate of reaction against temperature
6 Graph of results for rate of reaction against time
7 Graph for concentration results
8 Graph and table of typical results
9 Conclusion and Evaluation…
10 End of evaluation
This investigation is about Rates of Reaction and what affects them. In this case I am going to look at hydrochloric acid and sodium thiosulphate, which is a precipitation reaction. I will be investigating whether a change in temperature affects the rate of reaction.
Sodium thiosulphate + Hydrochloric acid ?Sodium chloride + sulphur dioxide + water + sulphur
Na2S2O3(aq) + 2HCl(aq) -* 2NaCl(aq) + S(s) + SO2(g) + H2O(l)
A reaction will only occur where the particles of the reactants meet and combine. This is called the collision theory. Therefore it stands to reason that to increase the rate of reaction it is necessary to cause more particles to collide harder and make it happen more often. There are several ways to do this and these make up the variables for this experiment.
1) Increasing the temperature — Increasing the temperature of the reactants will provide the particles with more kinetic (movement) energy. This will make the particles move faster. The number of successful collisions per second will also increase; hence the rate of the reaction increases. More collisions have an energy greater than the activation energy. But, although the rate of reaction is increased, the amount of the products produced at the end will remain the same (this is a continuous, independent variable, which I will be testing).
2) Adding a catalyst — a positive catalyst will speed up a reaction. The catalyst provides surfaces, which the molecules stick to, and react upon. It also lowers the activation energy, which is the energy needed for bonds to be broken, and the reaction to occur) by reducing the initial energy needed. This increases the number of successful collisions, resulting in an increased rate of reaction. Catalysts are specific to certain reactions.
3) Increasing the surface area — This involves ?breaking up? the reactant into smaller pieces. It provides more opportunities for the particles to collide (for example, the reaction between calcium carbonate and hydrochloric acid. When the calcium carbonate is powdered, there is more of it in contact with the hydrochloric acid). In some cases, stirring also has the same affect.
4) Increasing the concentration — A more concentrated solution will contain more of the same particles, which will be more tightly packed. So, once again, there will be a much greater chance of successful collisions between the particles (In this case, this reaction is exothermic, as it gives out energy)
I will be using:
A conical flask
A piece of paper
A black marker
I shall set up the equipment as in the diagram on page 3, drawing a black cross on a piece of paper with the marker. I shall then fill the kettle with water, and heat the water, to the testing temperatures. I will place the 5cm? of Hydrochloric acid into a 50ml conical flask. When the temperature is correct (20, 30, 40, 50 and 60 degrees centigrade), I shall then add 25cm? of a mixture of sodium thiosulphate and water (the concentration of the sodium thiosulphate will be 0.25 molars, and this will remain constant during the experiment). Simultaneously, I will start the timer. I shall test each temperature two times and then take an average to ensure that the result is balanced and not just a result of a fluke. The results will be taken optically, as we do not have the chance to use a computer. I will keep the timer on until the black cross marked on the piece of paper has disappeared. To ensure my results are as accurate as possible, we will use a pipette to measure the sodium thiosulphate, when placing it in the beaker. I will try to keep my measurements as precise as possible.
(My Diagram for the experiment is on Page 3)
I will have to consider safety precautions, so I will wear goggles, and tie my hair back to prevent any hazards. I will also have to make sure the apparatus is stable.
I will obtain results from the other choice of experiments, which is on the variable of concentration.
I will also obtain ?typical results?, to compare my results.
I predict that temperature is proportional to rate of reaction. I say this due to my research on the collision theory, etc. If the temperature is increased, the rate of reaction will also increase, as the particles will be given more energy. The rate of reaction will double each time the temperature is increased by 10? C (which is what happens according to my typical results, and according to more information given to me by my teacher). Also, for the results I will obtain for the concentration experiment, I predict, as the concentration is increased, the rate of reaction will increase. Finally, I predict that the stronger reaction will be that of temperature as at a higher temperature, there will be more particles colliding with enough energy to make the reaction happen; the activation energy.
Below are my results for the experiment.
Temperature (?C) Concentration of the sodium thiosulphate solution
Thiosulphate Volume of Na2S2O3 and water Volume of Acid
(cm?) Time (1) for cross to become obscured
Time (2) for the cross to become obscured Average Rate of reaction
20 0.25 m 25 5 94.6 87.9 91.24 0.0110s
30 0.25 m 25 5 74.2 59.4 63.86 0.0157s
40 0.25 m 25 5 19.57s 20.72s 20.15s 0.051s
50 0.25 m 25 5 19.10s 16.72s 17.5 0.056s
60 0.25 m 25 5 12.0 11.4 11.5 0.087s
(The graphs for these results are on pages 5 and 6)
These are the results for fellow pupil Jugal Patel, who completed the experiment for concentration, and how it affects the rate of reaction.
Volume of H2O Concentration of
Volume of acid
(cm?) Time (1) for cross to become obscured Time (2) for the cross to become obscured Average Rate of reaction 1/t (/s)
50 0 0.15m 5 53.48s 56.03s 54.76s 0.018s
40 10 0.12m 5 63.21s 65.42s 64.32s 0.0156s
30 20 0.09m 5 108.00s 103.47s 105.79s 0.009s
20 30 0.06m 5 154.36s 153.09s 153.73s 0.0065s
10 40 0.03m 5 350.07s 348.59s 349.33s 0.0029s
(And for comparison, a graph for these results is on page 7)
Upon looking at my results and graph, I do not see a clear pattern emerging. Referring back to the secondary evidence of typical results, I see what should have occurred (this is on page 8). My results do not prove my prediction, exactly, either. I said the results would be proportional, which was correct. However, I also said the rate of reaction will double as the temperature is increased by 10?C. This is because the particles of the reactant will be provided more kinetic energy, therefore, they will move faster, causing the rate of reaction to speed up. This is not confirmed by my results. At 20?C and 30?C, the rate of reaction seems to increase fairly steadily. But once we went up to 40?C, the rate of reaction increased dramtically from 0.0157s to 0.51s. A human or experimental error must have caused this to happen. At 50?C, the rise seems to be steady again, going from 0.51s to 0.56s. Acording to my prediction, and my typical results, this rise in rate of reaction is very small, at this stage. And at 60?C, the rate of reaction is 0.87s, which seems to be too high the temperature. My prediction that temperature would be the quicker rate of reaction was correct. Comparing Jugal?s results to my results, I can see that the rate of reaction using the highest concentration was only 0.18, compared to 0.87. This steeper graph can be explained by saying that were plenty of both reactants in the solutions tested. Faster collisions will only occur when the temperature is increased. In fact there was enough to support a much faster reaction than the one, which occurred. Because there were enough particles, the most important factor became the activation energy. By 40? many of the particles had reached activation energy. They then gave out heat themselves and so speeded up the reaction causing the large increase after 40?. However the collision theory can still be applied to both variables because when temperature/concentration increases, so does reaction rate. We used 0.25 molars of the sodium thiosulphate, and the highest concentration of the sodium thiosulphate was 0.15, which is contains a lot less particles.
No, not all my results were accurate. There are many ?strange? results in my experiment. This could all be blamed by human error and experimental error. Although during the experiment we were not aware of the errors, they have shown up quite clearly now. The method we used, could be improved by taking quite a number of measures. Below, I have listed what I think has been done ?wrong?, and what could be done to improve it if I repeat the experiment :
The temperature of the sodium thiosulphate was not measured. The colder acid may have bought down the temperature of the hydrochloric acid.
We conducted the experiment near window, and used natural light. This may also have affected the experiment as clouds were continually passing over the sun. An artificial source of light would have been more accurate.
We used a thermometer to measure the temperature. It would have been more accurate to use a water bath.
I personally don?t think that we gained a fair average. We planned to repeat each one 3 times, but during the first lesson, but we realised we wouldn?t have enough time to complete each experiment three times, so we had to limited it to two. Had we not made all the experimental errors I have listed above, we may have had more accurate results.
If I were able to extend my results, I would perform the experiment again, making all the adjustments mentioned above. I would also:
1) Do an experiment for concentration, as from the results I have I cannot tell whether they have been made up or not.
2) For the temperature experiments, I would use data-logging to be extremely accurate.
3) And once again for temperature, I would do the experiment up to 80?, to extend the results. If it had been possible to test 80? on the computer, I might be able to see the temperature at which all of the particles have reacted and the reaction stops
4) Finally, I would try adding a suitable catalyst if there is one to use.