The Effect of Temperature on the Rate of Reaction of Sodium Thiosulphate and Nitric Acid

The Effect of Temperature on the Rate of Reaction of Sodium Thiosulphate and Nitric Acid
Planning Aim The aim of this investigation is to find out and observe how the temperature affects the rate of reaction. I am going to investigate the rate at which the solutions of nitric acid (HNO³) and sodium thiosulphate (Na²S²O³) turn cloudy (when mixed together), when the temperature is changed. Variables In this investigation I will only have one variable: ? The temperature of both solutions (sodium thiosulphate and Nitric acid), so that I will be able to see the affect of temperature on the rate of reaction. The temperature will be measured in Celsius. Fair Test In this investigation I will keep the following constant: Ÿ The volume of sodium thiosulphate, at 20cm³ (16gl), so that the results will be consistent; Ÿ The volume of nitric acid, at 5cm³, so that the results will be consistent; Ÿ The volume of water, at 30cm³, so that the results will be consistent; Ÿ The same apparatus all the time, so that human error can help to be ruled out; and Ÿ The same crossed paper for each test, so that a fainter or bolder cross won?t be used.
If that happened then the results won?t be consistent. Another way in which I will keep this a fair test is by repeating the experiment 3 time for each temperature. I will also carry out the experiment indoors (with the lights on at all time during the experiment), so that the weather won?t effect the temperature of the experiment. Not only that, after every experiment I wil have to wash out each of the apparatus, thoroughly, so that the solutions won?t be able to get contaminated, via the apparatus. In order to make these results precise and reliable I will measure all the solutions with accuracy and I will try to time the reaction as precise as I can (by starting the time as soon as I pour the solutions in and by stopping the timing when the cross is absolutely obscure, by the sulphur suspended in the air). If I keep all of these variables the same, my results will be very precise. Range of Readings When I carry out the experiment, I will need to take various readings for my results. If I take a small amount of readings, I will not be able to show that my results are accurate. But if I take too many readings, I will just be wasting time and it also won?t be necessary. I think that 4 readings are enough to get consistent results, but if I want to be as accurate as possible, then I must repeat each experiment 3 times. This mean that all together I will have to record 12 readings. There will a table, which will be made up of 4 different temperatures: ? 20?C; ? 30?C; ? 40?C; and ? 50?C. They will contain 3 different time tries, the average time and the rate of reaction. It will also have the volume of sodium thiosulphate, nitric acid, and water. I decided to have the volumes of the solutions, because of my preliminary work. In my preliminary I found out that at room temperature, the time was 121 seconds. And I repeated the experiment at 40?C, and the result was 50 seconds. These times weren?t too fast or too slow, they were just right. If they were to fast, then I would have time, to time the reaction. And if they were too slow, then I would just be wasting precious experimental time. Prediction & Justification From my preliminary work, I believe that if you increase the temperature of both solutions, the speed at which the reaction takes place will also increase. This is all due to the factors which effect the rate of reaction. The rate of reaction varies greatly. Some chemical reactions, such as explosions, happen very quickly while others like rusting, occur very slowly. The factors which effect the rate of reaction are (all factors increase the number of collisions): Ÿ Temperature, because if the temperature is increased, the movement of the particles will also increase; Ÿ Concentration, because if the solution is made more concentrated, it means that there are more particles in a certain area, which therefore means that the collisions between each type of particle will become more likely; Ÿ Adding a catalyst, because a catalyst works by giving the particles a surface to stick to, where they can bump into each other; and Ÿ Surface area/particle size, because if one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area. That means that the particles around it will have more area to work on. The rate of reaction is the speed or velocity of a chemical reaction. This is calculated by using the formula, where T is time, which is me measured in seconds: 1 T The one that I am going to be investigating and explaining about is: temperature, as I state before. Changes in temperature, change the kinetic energy of the particles and therefore the numbers of successful collisions. If there is enough kinetic energy then the bonds between each atom will break (going from a liquid to a gas). For a reaction to take place molecules must collide with each other. When they do so, they must have enough energy to cause a reaction. So in order to cause a reaction, there has to be enough energy, within each of the different types of particles, to collide with each other. Temperature helps to do this, because by increasing the temperature of the substance the kinetic energy also increases. The two theories that affect temperature and the rate of reaction are the kinetic theory and the collision theory. The kinetic theory states that the positioning and movement of particles in a substance increases if the temperature increases. Therefore, increasing the temperature, increases the energy between the particles and makes them move around a lot more and collide more often. If this is done successfully, then the collisions should have no problem passing what the statement says in the collision theory. That statement is simply: particles have to collide, as well as have enough energy to break the bonds, in order to react. So as I said before, increasing the temperature (or the other factors) increases the rate of reaction speed. I can also predict that the graph below shows how I think the temperature will effect the rate at which the sulphur is produced, when nitric acid and sodium thiosulphate are mixed together: [image] [image] To find out the reasons for the temperature, effecting the rate of the reaction, I used a couple of secondary sources: ? Key science ? Chemistry by Eileen Ramsden; and ? gcse Chemistry ? The revision guide by Richard Parsons. I also used the internet and search engines such as: Ÿ Google; and Ÿ Yahoo. Method Firstly I will need to collect all the equipment and construct it as below: And I will need to put on the safety goggles, before I start the experiment. The reason for this, is that: sodium thiosulphate is corrosive, and if it gets in your eye then it may blind you. Next I will test the stopwatch to see if it is working properly. If I didn?t do this, I would press the button , to time the reaction, and it wouldn?t start timing. Then I would have to re-measure the solutions and heat them up. That would be very time consuming. After that, I will measure 5cm³ of nitric acid and pour it into an empty boiling tube, which I will then place in a test tube rack. I will also measure 20cm³ of sodium thiosulphate and 30cm³ of water. I will pour them both into an empty boiling tube (these two together will not react) and place the boiling tube into the same rack, as the one with the nitric acid. I will also place a thermometer in one of the boiling tubes. Then I will place the rack into the water bath, which will have already been heated up to 40?C. I will leave the 2 solutions to rise to a temperature of 40?C, for about 5 minutes. Meanwhile, I will get the stopwatch and the conical flask ready. I will also marked a black cross on a spare piece of paper, so that the reaction (which will take place in the cronical flask) can be position on top of it. Afterwards, I will take the two boiling tube out and pour them both into a cronical flask, which will have already been placed onto of a black cross, and time the reaction as soon as the last drop is added to the mixture. When the black cross is obscured, I will stop timing and record the time in the table, which I will have already draw up. I will repeat this experiment another 2 times. I will also do exactly the same thing with 30?C, and 50?C, but when I do 20?C I will need changed the water bath to a beaker filled with cold water. This is because the water bath will only heat up from 30?C. Obtaining Evidence Results [image] Anomalies results: 40.25 35.82 Volume of sodium thiosulphate: 20cm³ Volume of nitric acid: 5cm³ Volume of water: 30cm³ Observations All rate of reaction experiments have visible results and this experiment is no exception. When I added the nitric acid to the conical flask I immediately began to observe what was happening in the reaction. When observing the experiment, the changes I saw take place, were: the tone of the sodium thiosulphate and nitric acid solution. At the low temperatures, the solution became very foggy and misty but only after a fairly long time. At the higher temperatures, the solution became fogy very quickly and in both cases, the solution continued to get foggy until it was no longer clear or transparent. I could not see through the solution at all. The colour of the solution went from a clear colourless liquid to a dark yellowish colour. This was caused by the produced sulphur being suspended in air (Brownian Motion). The change in colour was smooth. Even though I did not see any gas given off, I knew that gas was being produce. This is because you could smell it. The smell was quite bad. There was also no sound made when the reaction took place. Reliable results To make my results reliable, (as I said in ?The fair test? section) I am going to repeat each temperature 3 times between 20?C and 50?C. That is 12 different results altogether. I will calculate the average of each temperature by the formula: (T1+T2+T3) 3 I will also make sure that each temperature is calculated as accurate it can be. As recording a result, past the required temperature, can mean unreliable results. This would make the entire investigation void, because of one result which wasn?t calculated correctly. Analysing and considering evidence Conclusion [image] [image] The line of best fit (in the first graph) is a downward curve, but it is also getting shallower, as the temperature gets higher. This shows that as the temperature is increased, the time of the reaction is decreased. This means that as the temperature increases there are more collisions between the particles, which will therefore make the rate of reaction faster. The line of best fit on the second graph is a upward curve. The curve gets steeper as the temperature increases. This shows that as the temperature is increased the rate if reaction also increases. From my results and my two graphs, I have come to the conclusion that if the temperature of a solution is increased, so is the time for the reaction to occur. The cross disappeared more rapidly as the temperature increased. I think this was due to, the increase of energy between the particles, which will then increase the speed of the particles, and in turn will create more and faster collisions. When this happens (in this particular experiment), it releases the sulphur quicker and in larger doses, which turned the solution cloudy therefore making the cross invisible. At the lower temperatures, the time for the cross to disappear was less because the particles did not have as much energy as they did at the higher temperatures. At these temperatures, the particles are colliding with much more energy and therefore the reaction, that releases sulphur, works faster and with more energy. This releases more sulphur at a much quicker rate, consequently increasing the rate at which the cross disappears. My original prediction was that if you increase the temperature of a reaction, then you the time of the reaction decreases. And, from looking back on my results, I can see that my prediction was correct, as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where the average time for the cross to disappear, at 30ºC, was 42.24 seconds and at 40ºC the average time for the cross to disappear was 36.17- a difference of 6.07 seconds. The particles were moving around with more energy; enough to break the bonds between the particles and for a reaction to take place faster, as the temperature increased. Evaluating Evaluation My experiment was performed with a few hiccups, but I managed to get round most of them and carry the experiment out properly. My results were very accurate, because all of the points on my graph were on the line of best fit, except for the two, which was slightly off. That means that I executed the experiment consistently, but not as accurate as I would of liked. The problems started with measuring the liquids. Sometimes I didn?t measuring them very accurately, which partly led to my results being inconsistent. On other occasions the liquid was just below or even above the exact line of measurement, which I was supposed to investigate. Another problem was keeping the reaction temperature steady. This was difficult to do, because as soon as you took the boiling tube out of the water bath, the temperature lowered, so then I had to place it back into the water bath and time the reaction again. This was time consuming, which meant that I could get more results from different temperatures. The last problem was actually timing the experiment. Humans will never time anything precisely, without the help of computers. That is why I would use a computer based simulation for this experiment, instead of the hand-eye co-ordination. This was probably the biggest problem, in the investigation, which caused my results to be a bit inaccurate. But overall the final experiment went well. All of these factors effected the outcome of the investigation (the results). I know this because I received two anomalies results. You can see these anomalies results below my table of results. But I managed to overcome these two results by redoing the specific temperature. I believe that I did get a suitable range of results for this experiment. I recorded results from temperatures of 20?C, 30?C, 40?C, and 50?C and I think that this is a very good range to see how temperature affects the rate of reaction. However, I feel that this also reduced the chance of knowing if anything changes, if the temperature reaches a certain point. Perhaps doing the temperature even higher or lower would improve my results but this is also quite dangerous, because I could get burnt, so I cannot really say that I could have improved the range of my results. Other investigations I could do to help support my conclusion, which are similar to this experiment are: ? Change in mass. Any reaction that produces a gas, when a solid is put into a solution, changes the solid?s mass, which can be easily measured on a mass balance. ? The volume of gas given off. This methods uses a syringe to measure the volume of gas given off. Overall, this investigation has been a very successful one. I feel my results were quite consistent and that my analysis was very accurate, under the time allocated. However I feel with extra time, I could of extend this investigation by experimenting with more temperatures, and also having different variables i.e. concentration of the acid or adding catalysts. For example: I could have 30cm³ of sodium thiosuphate, 20cm³ of water and 10cm³ of nitric acid.

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