I predict that as the temperature of the acid is increased the rate of reaction will increase. This means that my graph that will be drawn up in my analysis should have fairly strong positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as the temperature is increased. This can be justified by relating to the collision theory. When the temperature is increased the particles will have more room to move around, and have more energy and thus move faster. Therefore they will collide more often and with more energy. This is illustrated in my diagrams below:
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. An increase in the number of collisions can be achieved by increasing the concentration, pressure, or surface area. I think that the trendline in my final graph of results will look something like this, because there should be a maximum speed that the reaction can take place at, therefore the trendline should level off:
If the concentration of a solution is increased there are more reactant particles per volume. This increases the probability of reactant particles colliding with each other. If a solid is powdered down then there is a greater surface area available for a reaction, compared to the same mass of un-powdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas.
Method
A beaker is half filled with hot water from a tap. The water is placed on a gauze on a tripod above a Bunsen on a blue flame and the measuring of acid placed inside the water bath in a test-tube. The water is heated to the necessary temperature (Room Temp. to 60°C) then the test tube is taken out and the acid is poured into a Beaker, along with the Sodium Thiosulphate. The time it takes for the X to disappear is timed and recorded. The experiment is repeated using all the temperatures. The entire procedure is then repeated for more accurate results.
Repeated results will be recorded and averages will be taken to improve the credibility of the findings, and to compare to my original prediction. The repeated results will help to give more average results, and will therefore give a good summary of the experiment. However if one set of results is entirely different to the other, a third experiment should be performed to replace the anomalous set of results.
Safety – A pair of goggles will be worn during the heating part of the experiment in order to protect the eyes. When handling hot beakers and measuring cylinders a pair of tongs will be used. A gauze and heatproof mat will be used while heating to avoid any damage to the equipment. Also, the acid will be heated using a water-bath, as heating acid directly can be dangerous. A yellow flame will be used when the Bunsen is not in immediate use.
Fair Test - In order for my findings to be valid the experiment must be a fair one. I will use the same person (Me) standard each time for judging when the X has disappeared. I will make sure that the test tube for the HCl will remain the same for each test. During the heating stage of the experiment, a blue flame will be used throughout. Also the same Bunsen burner and gas tap will be used throughout the experiment. All of these precautions will make my final results more reliable and keep anomalies at a minimum and therefore make the entire investigation more successful.
Obtaining Evidence
Analysis
I will recap the collision theory briefly because the collision theory is in line with my prediction. For a reaction to occur particles have to collide with each other. Only a small percent actually result in a reaction. If the number of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the number of collisions can be achieved by increasing the concentration, pressure, or surface area.
In this experiment I have found that as the temperature and concentration is increased the time taken for the reaction to take place decreases. This means the rate of reaction increases as it takes less time for a reaction to take place. This fits in nicely with the collision theory, which, as stated above, says that as a chemical is heated up, the atoms slightly spread out, and have more energy. If the particles have more energy and more space to move around, then there is more chance of them colliding and therefore more chance of a reaction to take place. In the experiment the time taken for a reaction to take place started to decrease roughly at around 10 seconds, and became slightly less for every 10°C increase in temperature, until it started to stay the same. I think that this is where the particles are undergoing the maximum collisions, therefore not allowing the chemicals to react any faster. There is also a trend in the increase in rate of reaction as the temperature increases.
I found that my prediction was correct, and that as the temperature increased, the rate of reactions increased, which means that the number of collisions also increased. The number of collisions levelled off near the highest temperatures, as the particles were releasing their maximum energy, and were causing their maximum collisions, which is why the times or the rates of reaction ever increased after levelling off. This therefore backs up my prediction in what I thought would happen in this Investigation.
Evaluation
I think that my results are fairly accurate as I have no outstanding anomalous results. This shows that the equipment I used was efficient and the averages were very close to the original times, which shows that the tests were very successful. Any slightly out of line results could have been because of the temperature of the Hydrochloric acid may have slightly decreased by the time it was taken out of the water-bath to the time it was put in the beaker with the sodium, I was as quick as possible, so as not to let the temperature decrease. I also kept all of the methods of the experiment the same throughout all of our tests. Although I feel that my investigation was successful, there are always ways that the tests could be improved and expanded. Some of these are by using more accurate measurements, like measuring the temperature to a tenth of a oC, or by measuring the time taken by a the thousandth of a second instead of just a hundredth. Also, clean and accurate working apparatus that is in a good condition could be used for more precise results. I could expand this investigation by, as I mentioned earlier, using Acid of a Temperature under room temperature and above 600C to test whether the maximum collisions in the reaction is the same, or whether there is a different outcome.
