The rate of reaction between sodium thiosulphate and hydrochloric acid
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Rates of Reaction Investigation PLAN Aim: An investigation to find the effect of changing the concentration on the rate of reaction between sodium thiosulphate and hydrochloric acid. Safety Precautions * Tie hair back * Wear goggles at all times * Be careful when using the chemicals * Do not run * Do not sit down during experiment * Tuck in bags and stools. Fair Test To make the experiment a fair test, it must be carried out by: * Using the same equipment each time * Keeping a control to determine whether the experiments have worked correctly * Making sure all of the independent variables are controlled, except ONE which is changed * Make sure the stopwatch is always started at the same time for each test * The temperature should be the same for each test done Prediction I think that the higher the concentration of sodium thiosulphate solution, the quicker the cross will disappear. This means that the graph will have positive correlation. This is explained by the collision theory. Particles have to collide for a reaction to take place. However, only particles with enough energy manage to cause a reaction when they collide. The activation energy is the minimum amount of energy that a particle needs to cause a reaction. The activation energy depends on the reaction, but if the frequency of the collisions increases, so will the reaction rate increase. If the concentration of a solution increases, then the likelihood of collisions between the reacting particles is higher. The Collision theory states that the rate of reaction relies on how often and how hard the reacting particles crash into each other. There are four methods that increase the rate of reaction * Varying the temperature of the reactants * Changing the surface area of solid reactants * Adding a catalyst * Varying the concentration of the reactants in solution However, the reaction rate between sodium thiosulphate and dilute hydrochloric acid can only be altered by changing the concentration or the temperature of the reactants.
This could affect the experiment as it would end up changing the concentration of the solution, resulting in either a quicker or slower time. This means that if there are more reactant particles between the water molecules these would make collisions between the reactant particles a lot more probable, and vice versa. Due to this, I will use a burette for accuracy in measuring. If the temperatures of the solutions change, then this could affect the rate of reaction, resulting in different times and a quicker reaction. When the temperature is increased the particles will have more energy and therefore move faster. Consequently they will collide more often. Particles with more energy are more likely to overcome the activation energy barrier to reaction and hence react effectively Also, once the cross has disappeared, it is hard to stop the stopwatch at the precise moment, which could make the time off by a few seconds. For my results I am planning to get a good range of concentrations, from 1.0-0.2, thus making my graphs more accurate and enabling me to get a better analyse and evaluation. I will time how long it takes for the cross to disappear, and then I will find the reaction rate from this. I will repeat any anomalies that appear in my results to make my overall results more reliable. ANALYSING Results: Water Sodium Thiosulphate mol/dm³ Time (s) Rate of reaction 1/S concentration 1 0 50 1.0 15.92 0.063 2 5 45 0.9 17.75 0.056 3 10 40 0.8 20.58 0.049 4 15 35 0.7 23.14 0.043 5 20 30 0.6 26.34 0.038 6 25 25 0.5 29.75 0.034 7 30 20 0.4 38.59 0.026 8 35 15 0.3 47.52 0.021 9 40 10 0.2 74.13 0.013 The experiment with the concentration of sodium thiosulphate at 0.9 was redone, as the first result was an anomaly and did not fit in with the rest of the results.
They match my prediction by increasing the rate of reaction as the concentration gets higher. EVALUATING I think that my experiment has worked out well as I was able to attain good results that supported my prediction, and resulted in being able to have a good set of graphs with the correct correlation. Also, any anomalies that I had were repeated, so as to make my results more accurate. My results were accurate enough to use as I measured the solutions using a burette, making it more precise and therefore reliable. Also, the same equipment was used, and the temperature was the same for each experiment, meaning that this factor did not effect or change the results. To improve my experiment if I redid it, I would use a light sensor. The light sensor would pass through the flask to a receiver. At the point when no light can reach the receiver, then the time will be stopped. This is a lot more accurate, compared to trying to judge using the naked eye. I think that my method was quite precise and resulted in getting the best results possible with the equipment that was available to use. The measuring devices were accurate. An improvement to the method would have been to have done more repeats to make sure that my results were correct. One result that did not seem to fit the overall results was when the concentration was 0.9. The time increased by about 5secs, instead of just around 3secs, resulting in an anomaly in the results. This could have been caused either by using sodium thiosulphate from a different burette which would have a different temperature or maybe just human error and not stopping the stopwatch and the correct time. An experiment that could be done to extend the work would be to find out the effect temperature has on the reaction rate between dilute hydrochloric acid and sodium thiosulphate. This would be able to show which one has the larger effect of the reaction rate. ?? ?? ?? ?? 1
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