I have drawn a diagram of the experiment with the apparatus on another piece of paper. The apparatus that can be used is a light meter, but as I am not allowed that amount of time, I will not be using one, along with a burette, to measure the hydrochloric acid and sodium thiosulphate.
Method
As I am doing two experiments, testing two different factors that affect the rate of reaction, there will be two different methods, but some things will remain the same. The first experiment changes the concentration of the sodium thiosulphate as this in a surplus quantity then the hydrochloric acid. I will measure 10 cm³ of hydrochloric acid, which will remain the same amount throughout the varying concentrations. The water will be distilled water and will be measured in a larger beaker, 50cm³, along with the sodium thiosulphate. The concentrations I will be using are, water to sodium thiosulphate, in the ratio 0:40, 5:35, 10:30, 15:25, 20:20, 25:15, 30:10, 35:5, 37.5:2.5. These concentrations will be used after a preliminary test was taken to allow myself to see how long it took for the concentration, which was the most dilute. Here is a table, which allowed me to see which concentrations were the best.
The total amount of solution must not exceed 50 cm³. A cross will be drawn on a piece of paper, from which the same person will be able to tell when the reaction has been completed. The sodium thiosulphate will be in the beaker and the hydrochloric acid added. The time for the precipitate to form will be noted.
In the second experiment, we will see how temperature affects the rate. Heating the sodium thiosulphate along with the water will do this. It is too dangerous to heat the hydrochloric acid. The solution will be heated to the required temperatures, which are 20ºC, 30ºC, 40ºC, 50ºC, 60ºC, 70ºC, 80ºC, and 90ºC. A preliminary experiment was taken to determine these temperatures. Here it is:
The concentrations of the liquids will be kept the same at 10 cm³ for hydrochloric acid, 30 cm³ of water and 10 cm³ of sodium thiosulphate. The sodium thiosulphate and the water mixture will be heated and then when the required temperature has been reached, the acid will be added. The time taken for the precipitate to from will be noted. In both experiments, the stopwatch was started the second the acid touched the sodium thiosulphate solution. No control will be used, but the fact that the same person will be watching the cross ensures consistency.
To make the experiment fair, I will use the same cross with each experiment, the same person will be watching the cross, the same size beaker will be used, the same person will measure the solutions and the same size beakers will be used. Only distilled water and the same acid will be used in both experiments. For the concentrations experiment, the same temperature will be used to ensure fairness. The temperature will be kept at room temperature, 20°C. I will conduct the experiment in the same room and in the same part so the outside factors that might affect the experiment will all be the same. The apparatus will be washed out with distilled water so that the new experiment is fair. I will do the experiment twice to get an average and a more accurate result. To allow reliability, the repetition of the experiment will allow me to see if there are any anomalous results, which I will repeat. Also I will draw a best-fit line on my graphs to see if there are any anomalous results, which will show me if the experiment is reliable.
To ensure safety in the experiment, I will wear goggles to protect my eyes. I will not heat the acid, as this is dangerous and I will make sure that the acid is not spilled, as it is corrosive. The sodium thiosulphate will not be spilled either, as it is dangerous. When the temperature experiment is undertaken, I will wear some rubber protectors so that I do not burn myself. I will stand up so if the beaker was to fall I will be able to move out of the way. Stools will be kept under tables to stop people from falling over.
In my results I will put the rate of reaction. This was measured by dividing time by 1.
Conclusion
Looking at my results I can see that they follow trends that will allow me to ascertain whether my prediction follows or not. The concentration graph gave me a very nice best-fit line, which allowed me to prove that as concentration doubles, rate of reaction doubles (see lines on graph). This fits in with my prediction, so backing it and also fits in with my theories. The Collision Theory works best in this, as there are more particles per square unit, meaning a greater chance of a collision, but also a greater chance of a successful collisions as there is double the amount of particles. At a low concentration, 2.5 cm³, the graph shows that there is barely a rate of reaction, but my results increase at a steady concentration, allowing me to draw an almost proportional best-fit line. At a concentration of 40 cm³, we see that the best-fit line is starting to level off. This means that the acid is becoming too saturated; there are too many sodium thiosulphate molecules in ratio to the hydrochloric particles. This means that the hydrochloric particles will all have reacted, but not all of the sodium thiosulphate particles will have reacted, leaving a surplus. The Collision Theory or Kinetic Theory can do nothing to cause the rate of reaction to increase. From my graph, I can see that at 40 cm³, there were the most amounts of collisions, but at 2.5 cm³, there were so few particles of sodium thiosulphate, there was a lower chance of a collision between the molecules. This followed my prediction, as I said that at 2.5 cm³ the rate of reaction would be much lower. I have explained before how my results prove the theories behind my prediction for this experiment. The heat given off by the experiment did nothing to change the rate of reaction, as the reactants were so dilute. The particles in the solution had to hit in a particular manner, and with enough energy to cause a successful reaction, otherwise the rate went down.
There are two anomalous results, which I have circled. They do not follow the pattern set by the best-fit line. The reason for them is that in both repeats of the experiment, it came up with the same inequalities, so in my results table there are no anomalous results, but once I plotted the average onto my graph, they showed up. It could be due to method carried out and the accuracy of the apparatus used. As we used measuring cylinders, it was extremely hard to come up with the same measurements all the time. This allowed discrepancies to crop up in the graph rather than the results table.
My second graph again follows a similar trend, allowing me to draw a best-fit line. I have drawn lines on showing that the rate of reaction doubles after 10ºC increase in temperature. This fits in with my prediction and also my theories, especially the Q10 factor, which states that raising the temperature by 10°C, usually doubles the rate of reaction. This also ties in with the Kinetic Theory, which states that if you double the heat you double the energy. It is known that if there is an increased amount of energy on particles there is going to be greater ratio of successful collisions. My graph shows that at low temperatures such as 40ºC, the rate is only 0.029s-1, but at 90ºC it has increased to 0.014s-1. Thus showing that with increased energy the rate will increase. This also ties in with the Collision Theory, which shows that with this extra energy they are more likely to overcome the activation barrier inhibiting it form fully reacting and causing the rate to increase. Unlike concentration there is nothing to stop the rate from increasing, so the graph is directly proportional and does not taper off. My graph has followed my prediction, and has also followed the theories backing my prediction.
There is one anomalous result that I have circled. This is likely to be the cause in a discrepancy caused by the apparatus as I have stated in the first part of my conclusion. As there are not many factors to affect temperature, so the line will go on indefinitely. Also we did not manage to get to the temperature we wanted, as the acid brought the temperature down extremely, so the rate may be of a lower temperature.
The results I attained followed my predictions so it proved my theory, but they were not necessarily accurate as the apparatus used were not accurate enough to give me a precise result. As there were anomalous results it is true that the experiment was not that accurate otherwise all the results would follow a trend line. My results in my tables were reliable as they were all at least within three seconds of each other and they allowed me to draw an easily understandable best-fit line which allowed me to analyse my results, so I could attain the information to prove my prediction were almost correct. In both of my results, they were not that different that meant I could repeat them, but as I came up with the graph after the time I was allotted to do the experiments, I did not have enough time to repeat them.
I conclude that although my results were not entirely accurate, they did follow a trend that backed my prediction. I obtained enough information to see the affects of temperature ands concentration on the rate of reaction of this particular experiment.
Evaluation
The method I used was suitable, although I did get a few anomalous results in my graph. These anomalous drew me to the conclusion that the method was suitable, but it did have some major discrepancies. I followed the method accurately, but sometimes we were thrown by the rapidity of the experiment and were not prepared for the time to be noted. These anomalous results proved that the experiment was flawed, as I should have got perfect results. The personal reasons for why I may have got these results are because we used different acids and sodium thiosulphate over the days, so we were not sure whether we got the same result. There were some times when it was necessary to repeat the experiment as we did not note the time, this may have altered the results as then the beaker may not have been cleaned thoroughly. The inaccuracies, which may have occurred because of the method, were the fact that we did not use accurate measuring devices, of the acid, sodium thiosulphate or the light. The methods that were used led to inaccurate and unreliable results.
If I were to improve the results I would ensure that we used a burette to measure the acid and the sodium thiosulphate. This would add accuracy to the experiment and the results. Also I would use a light meter, as this would give an even more accurate result. I have enclosed a graph using a light meter on different concentrations. It gives a very detailed graph, which can easily show a similar trend to prove my theory. We can see where the reaction goes fastest and where it has finished. It also gives an accurate amount of light concentration tha6t has been stopped rather than the cross which was not always accurate as the person looking could not always be sure.
My results were reliable as they allowed me to come up with a suitable best-fit line and firm conclusions from this. They were not accurate as they contained anomalous results that were caused by the inaccuracy of the method. I have talked more about this in my conclusion. I took enough results to tell me whether there were any anomalous results, but it would have been more accurate if I had taken three results rather than two as this would ascertain whether the two results were inaccurate or not. The range I used was good enough as well as I did it from the preliminary experiment, which showed me which experiments took over a certain amount of seconds. This gave me the range, which ranged from extremely low concentrations to high enough showing how the rate is affected by the concentration after a certain amount. Also the temperature allowed me to come up with valid results from my graph. My trends allowed me to see that a high concentration will have no affect on the rate of reaction, but a high temperature will increase it.
If I had more time I would see if I used a burette and other accurate measuring devices, how they differed from my results. I could also do three results to attain an accurate rate of reaction. I would also extend the temperature to see how slow the rate is at a very low temperature and how extremely high temperature affects the particles and if they will react differently.
If I extended this experiment I would see how other factors affect the rate. I would see how catalysts affect it, increasing pressure and increasing surface area. This would be done by either putting the gasses into smaller spaces or cutting the solids into smaller pieces. I would to different sizes to see if a very small piece of substance would have an differing result from a piece of substance slightly larger. Also I could see if the rate of reaction differs between states, solids, liquids and gases. I could test the situation it is in, if gravity has any effect on it, or if a high amount of pressure, like under the sea. This experiment helped me to learn a lot about rate of reactions and the factors. It also helped me to understand how to improve the method, as it was not entirely accurate.
It is important to learn about rates of reaction as they come into everyday life. They can allow rusting to occur at a faster rate, but they also help in making chemicals like in plastics, medicines and explosives. Also catalysts are used to crack kerosene into octane and ethanol so there is a higher percentage of gasoline for companies, from crude oil.
