The reaction will only occur where the particles of the reactants meet and combine together. The collision theory also states that as you increase the rate of reaction, the collisions between particles are bound to increase vastly. A general reaction consists of collisions between molecules or atoms that have the ability to react in response to collisions. The bonds between atoms are formed in such a way that it requires the atoms to stay close together. If one group of atoms is to from a new bond with another, it can only be done if the atoms are close enough to share the electrons. Once the particles collide to produce a product, they are known as effective collisions. This can only happen with great speed, energy and force so it can break down the bonds in the molecules. All though this bonding method sounds easy (as all atoms are closely packed together), they are not always successful. These are known as ineffective collisions. The particles just hit the other atom then rebound straight off it instead of bonding with it. Temperature is the factor that gives the molecules the energy to collide more frequently at fast rates. This basically means they will be less time between each collision so the frequency of collisions will increase. If the collision occurs more frequently and violently, it will immediately result in an effective collision. The more higher the temperature, the more frequent and violent the collision becomes and the more effective it will be. This clearly shows that the temperature affects the rate of reaction positively as it increases the heat which leads to the atoms vibrating more frequently so they are moving about more (Kinetic energy) so there would be a higher chance of a successful collision leading to a faster rate of reaction.
Preliminary Test
Before I got onto the main aim of my experiment, I needed to carry out a preliminary test. I did this to find out what suitable ranges of temperature I should be using for the final experiment. From this test, I hope to find out the highest temperature that does not make the reaction take place too quickly, to make sure that the lowest temperature does not make the reaction take to long and to see if the Sodium Thiosulphate reacts within a suitable time. I will also be analysing:
- The limits of the ranges of temperature used (Lowest and highest time)
- An appropriate volume for the reactants (What volume of chemicals to take)
- The concentration of Thiosulphate needs to be taken (The amount of concentration)
- The concentration and volume of the Hydrochloric acid (The amount of concentration)
I am looking for a reaction that lasts up to 3 minutes. If the sodium thiosulphate is added to water that has a very high temperature, it will disassociate before the hydrochloric acid is added. Therefore, the preliminary test will help me find a suitable temperature.
From the pre-test, I have learnt that the higher the temperature the faster the reaction between sodium thiosulphate and hydrochloric acid will be. I would need to heat the sodium thiosulphate about 2 oC more than I need to because the hydrochloric acid is cold, so when I add it to the heated sodium thiosulphate it will cool it down by a couple of degrees, so if I needed the temperature to be 34 oC I would have to heat it to 36 oC, this was a problem I had while doing the pre-test. Another problem I had was when I heated the sodium thiosulphate it got heated too much so I had to wait for it to cool down. When I do the experiment again I will use some ice to cool it down faster to get it to the temperature that I need it to be in order to complete my investigation. From my preliminary investigation I have decided to continue using 50cm³ of Sodium Thiosulphate and 5cm³ Hydrochloric Acid
The reaction that occurs produces sulphur dioxide, water and sodium chloride. It can be shown by this equation:
Apparatus List
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3 Beakers: HCl, Na2S2O3 and water
- Safety goggles
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Bunsen burner: to heat the Na2S2O3 to the temperature I need
- Heatproof mat: safety
- Gauze: to place the beaker of boiling water upon
- Tongs: to safely pick up the beakers
- Tripod
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Water bath: to heat the Na2S2O3 to the temperature I need
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Ice: to cool the Na2S2O3 to the temperature I need
- Stopwatch: to record the time it took for the reaction to take place
- Thermometer: to measure the temperatures I need
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2 measuring cylinders (prevents contamination): to measure the HCl and Na2S2O3
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an X on a piece of paper
Safety
Safety is a big issue when carrying out any experiment. Safety precautions should be followed when doing all experiments so no accidents occur. In this particular experiment, I will be looking out for certain safety aspect. I will be wearing safety goggles to keep my eyes protected just in case of a minor accident like the solution splashing out. If any chemical accidentally goes onto my hand or eyes, I will immediately go to the nearest sink and wash it out so no irritation is caused. I will keep all my equipment I am using in the centre of my table so it does no fall on the floor and break and cause further accidents. I will keep the window open so the fumes can escape and so we don’t inhale the chemical into our system, which can cause serious problems. Fair test In order to make my experiment a fair test, I will carry out the same procedure for each of the following factors: Following these rules will enable the test to be carried out fairly and no foreign ions will be able to enter your solution and ruin the end result.
Method for my Experiment
- At the start of my experiment, I will gather all the apparatus that I will be using and place it on the clear desk where I will be working. I will then put on my safety goggles.
- I will then measure and concentrate the reactants in a measuring cylinder.
- Once the Sodium thiosulphate and hydrochloric acid are set into two separate measuring cylinders and the 40ml of water is in the conical flask, I will start heating the water in the kettle.
- I will place the conical flask with the water in it and the 10ml of Sodium thiosulphate, inside a beaker that has boiling water inside it.
- Once the water and Sodium thiosulphate in the conical flask has reached its required temperature, I will take it out of the beaker and place it onto an ‘X’.
- I will add the HCl and then record the temperature using a data logger straight after I have added the Thiosulphate. I will then stir it three times and start the stopwatch.
- I will observe the reaction and I will immediately start the watch as soon as I have mixed the reactants and stop it as soon as the ?X? has disappeared.
- Once the reaction is finished I will take down the temperature and record it. I will also record the time taken for the reaction that lead to the ‘X’ disappearing to take place. It is only a complete reaction once the ‘X’ has completely disappeared.
- I will record the result for each temperature three times so we can get a reliable average time at the end instead of relying on one result. This will also help us to view any errors that take place that affects the overall result.
- I will gather all my data into clear tables and I will define my results on a graph. I will do separate graphs for each of the three experiments so I can analyse them separately, and then I will plot the averages onto one graph to compare their overall result together.
In order to make a fair experiment the X should always be the same size and drawn with the same pen; ideally always the same X would be used. The temperature will be taken at the start and end of each experiment and an average taken. This is because by the end of each experiment the temperature of the solution will have cooled and the temperature taken at the beginning would be inaccurate. Each experiment will be repeated at least twice and an average will be taken. This will ensure that results that are inaccurate will be noticed and the time will be as accurate as possible. The only variable in the experiment will be the temperature; the amounts of HCl, Na2S2O3 and everything else will be kept constant. The apparatus must be carefully cleaned out after each experiment because just one drop of HCl in Na2S2O3 can contaminate it and make all the results inaccurate, as I found out in my preliminary tests.
Graphs
This graph shows the 1st attempt at which I done the experiment. It shows that as the temperature increases, the rate of reaction (time) also increases. The rate of reaction starts off at a steep rate and eventually decreases and stays at a steady rate. The starting time temperature is almost a fifth of the reaction time so that shows the low temperature took a long time to react fully. There are 2 anomalous on this graph at 30 & 35 degrees.
2nd attempt
This graph shows the 2nd attempt at which attempted the experiment. This also shows that as the temperature increases, the rate of reaction (time) also increases. The rate of reaction looks starts off at a steeper rate than the first attempt and eventually decreases into a steadier rate. This graph shows that in the middle of the experiment, the temperature was two thirds of the time. This shows that the rate of reaction has decreased compared to the start/lowest temperature (explained in 1st attempt). There is only one main anomalous that stands out the most at 35 degrees. This could be due to the container or data logger not being cleaned so it added more particles into the reacting solution so it took more time for the full production to take place as more particles needed to collide and react..
3rd attempt
This graph shows the 3rd attempt of the experiment. It shows that as the temperature increases, the rate of reaction (time) also increases. The rate of reaction starts off at a steep rate and eventually decreases and stays at a slow steady rate. This shows that at the highest temperature, it is almost a quadruped of the time. This shows that the highest temperature increased the reaction speed vastly. This shows that the rate of reaction decreased dramatically overall as the temperature was decreased. This graph shows the average of the three attempts. This gives us an efficient result, as we are not just basing it on a singular result, but a multiple version test to make it fair and more reliable. It shows that just like the other graph, as the temperature is increased, the rate of reaction is also lifted. The main points that stood out in the previous graphs show that as the temperature increases, the amount of time taken for the reaction to take place increases vastly at different stages. This also shows the same result with the gradient showing the intercept at the different stages of A. B & C.
Analysis
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My results that I have recorded in tables have been transformed into graphs, as it is easier to observe the rate of reaction. They show a clear indication of how the temperature affects the rate of reaction. As I predicted, as the temperature was increased, the rate of reaction also increased. If I look at the graph backwards, I can back up this theory because as the temperature decreases, the rate of reaction also decreases. My scientific knowledge lead me onto the correct path as it taught me that it is the temperature that gives the particles the energy to collide more violently and frequently. As temperature increased for each reaction, the kinetic energy particles of the two reactants caused the particles to collide more often. The collisions came out to be effective and as the collisions widened on the scale, the rate of reaction also increased. My results show that when the temperature was within the region of 20C-50C, the time taken for the reaction to be complete decreased drastically on a steep slop but once we get to the region of 60C-70C, the time decreased at a steady rate, as shown on the graph. Although the experiment was successful, there were two anomalies, they did show up on the graph but they did not change the overall meaning of the gradient. The goggles were also slightly misty so it was hard for us to see clearly whether the cross had disappeared but we still got the result we wanted I will explain the situation fully in my evaluation. The cloudiness of the formed solution was formed by the sulphur in the compound thiosulphate. As the temperature increases, the time for the cross to disappear decreases, so the reaction becomes faster. The graphs both show this. The first graph is a curve and although I cannot find a formula from it, it would be a 1/x graph. The values of 1/time are proportional to the rates of reaction, and produce a straight-line graph with gradient 0.0008. From the straight line I can calculate an equation: y = 0.0008 x - 0.014. From 20C a rise of 10C approximately doubled the rate of reaction. From 40C, however, a rise of 22C is needed before the rate of reaction is doubled. This shows an increasing rate of reaction. The reaction is a precipitation reaction, meaning that the product of the reaction is a precipitate, which clouds the solution.
Evaluation
The results that I formed from this experiment seem fairly accurate as I followed all steps of my methods carefully and made sure I kept the correct variables the same. My preliminary tests helped me achieve my results as it gave me the accurate volume and temperatures that I needed for the sodium thiosulphate, hydrochloric acid and water for my final experiment. We focused very seriously when recording the results because we needed to be on time when we stopped and started the stopwatch and we needed to measure all the solutions as accurately as possible and combining them at the correct times. As I explained in my analysis, I carried out the experiment correctly but I accidentally made two errors towards the end of the experiment as I rushed it because it was nearly finished. When we got to the temperature of 30C, we forgot to wash the thermometer for our next temperature change so we used the same thermometer meaning the new solution may have had 1ml extra of Sodium thiosulphate + hydrochloric acid. This did not make it a fair test as this was unfair because not all temperatures had this treatment. Another error made was that we only changed the cross once and we left it there even though it was slightly faded and this is unfair as it would be easier for the cross to disappear because it is not as bold as it was at the start. We should have changed the cross as soon as it was getting slightly faded as it could have made all the difference but this did not affect the overall result on the graph. My mistakes did show up on the graphs but they did not alter the overall gradient as they were not major problems but it still wasn’t a fair test. The reason that we started at the highest temperature was because it was easier to use the boiling water for the high temperatures needed and you could have used the same water in the beaker because it would have cooled down by 5C by the time you finished each temperature. Doing this saves you time as you do not have to wait for fresh boiling water to reach a low temperature. Using the same temperature three times made this test more reliable as the selected temperature had the same room temperature. If you done all the experiment once and then repeated it all again for the second time, the room temperature is bound to change so it is fair to do it within the same room temperature. My results table show the before and after temperatures seem to decrease by a minor fraction of degrees. The reason why this happened was that I only heated the Sodium Thiosulphate (via the hot beaker water) and kept the Hydrochloric Acid at room temperature. Even though they were different temperatures, my prediction and result still seemed to match so I still feel that I have gained the correct meaning from this experiment. I did the experiment fairly well as I cleaned the thermometer, up to 30C, and I cleaned all the beakers and conical flasks with hot water after each temperature. The people in our groups were assigned their own tasks, like someone recorded the temperature, someone had the stopwatch and I was keeping my eye on the ‘X’ waiting for it to disappear. I remained as the person that watched out for the ‘X’ As I have different eyesight to the other members in the group so we thought the vision should stay the same. The goggles were slightly misty so it was hard for us to see clearly whether the cross had disappeared but we still got the result we wanted. Our group all got involved in keeping this a safe and effective experiment by following all the safety precautions that we set at the start of the experiment. We completed the experiment by ourselves and carried out the investigation by ourselves but we formed a group to make sure we all followed the correct procedure for the investigation.
Conclusion
I conclude that the temperature does affect rate of reaction - the higher the temperature the lower the rate of reaction. I can see this from my table (the lowest temperature has the highest reaction time - 100C took 77 seconds - and the highest temperature has the quickest reaction time - 650C took 4 seconds). I can also see this from my graph. This is because with more heat, the particles of sodium thiosulphate and hydrochloric acid have more energy. This causes them to move around more. Chemical reactions require collisions, and if two sets of particles are moving around quickly there will naturally be more collisions. However, the collisions require the particles to hit each other at a certain velocity, and if this velocity if not reached then the reaction will just not happen. So, at the higher temperatures, more of the particles were travelling at a high enough speed to collide and react. At the lower temperatures it was more difficult for the particles to collide. Only some were able to reach the required speed and react. At 100C the reaction took a very long time to occur. This was because there was not very much heat. Heat provides energy to the particles of reactants, and if there is not very much heat, the particles do not have very much energy. Because they do not have much energy they will not move around much, and will therefore not collide very often. Chemical reactions require a certain speed collision to react, and at this temperature very few of the particles collided, because of not moving around more due to lack of energy, because the heat was not very great. My results and evidence support my prediction very well. They prove the fact that temperature does affect the rate of reaction. My prediction was almost 100% correct, although I did not know that there would be a dramatic decrease in reaction rate on the lower temperatures. So I did make a good prediction.