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We will carry out an experiment to see how concentration affects rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

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Rates of reaction coursework Introduction We will carry out an experiment to see how concentration affects rate of reaction between Sodium Thiosulphate and Hydrochloric Acid. The equation for the reaction is= S2O3(aq) + 2H(aq) S(s) + H2O(l) + SO2(g) In order for a reactant to be broken down, the chemical bonds that hold the atoms together have to be broken by other particles bumping into them. The energy needed for this to happen alters from chemical to chemical, and this is called the ACTIVATION ENERGY. Increasing the temperature gives the particles more energy, and this makes them more capable of travelling faster and bumping into the bonds with more energy and breaking more, therefore breaking down the substance. Increasing the concentration of the substance also makes the reaction happen quicker, as this means that there are more particles, and in turn this means that more particles can react and more of the substances is broken down. Surface area also affects the rate of reaction. If the surface area is larger, then there are more particles exposed for reaction. The rate of reaction is the amount of time it takes for the reactants to disappear, and for a product to appear. There are five factors, which affect the rate of reaction; temperature - which we may encounter as the chemicals cannot be kept at a steady temperature. Pressure, but this is only in gases and gases are only being produced, not reacted; Surface area, but this is only with solids, and there are no solids involved in this reaction. Also there is concentration, which is the one we are investigating; and catalysts, which are substances that are used to speed up a reaction time. Catalysts weaken the chemical bonds in the substances, which makes it easier for them to be broken, therefore it is easier for them to be broken down. This means that the activation energy is lower. ...read more.


Concentration (Cm3) Temp (0C) Reaction time (seconds) Overall Volume (Cm3) of: Start Finish Experiment: Experiment: Thiosulphate Water 1 2 3 1 2 3 1 2 3 Average 0.2 50 0 19 19 19 18 18 18 25.0 24.8 25.1 25 0.18 45 5 19 18.5 19 17.5 18 18 26.1 27.4 26.2 27 0.16 40 10 18.5 18.5 19 18 18 18.5 27.9 28.6 28.1 28 0.14 35 15 18.5 18.5 18.5 18 18 18 30.6 33.5 33.0 33 0.12 30 20 18.5 19 19 18 18.5 18.5 39.9 39.5 40.2 40 0.10 25 25 19 19 20 18.5 18.5 19 46.5 47.5 47.9 47 0.08 20 30 19 18.5 18.5 18.5 18 18 56.1 55.4 55.9 56 Analysis My results show that when you halve the concentration of Sodium Thiosulphate, it takes a lot more time to react. This is because there are a lot less particles of Sodium Thiosulphate, so there are fewer reactions; therefore it takes more time for the product (a gas) to be produced, so it takes longer for the cross to be clouded over by the gas. In this experiment, the concentration halves twice; from 0.2 Molar to 0.1 Molar, and from 0.16 Molar to 0.08 Molar. This is so that I can justify my prediction. If it was only doubled once, it could be a fluke if what I predicted was right. There is a pattern that the lower the concentration of Sodium Thiosulphate is, the longer the reaction time is. This shows that concentration affects reaction rate in an inversely proportional way; the lower the concentration goes, the higher the reaction time gets. Conclusion From all my work, I have found that firstly, concentration is inversely proportional to rate of reaction, and that if you halve the concentration, the rate is doubly slower (It takes double the time to react) This is because, if there are a certain number of particles in a concentration (for example 0.2 Molar), then when you halve the concentration, the proportion of the particles with enough energy (activation energy) ...read more.


We could use equipment to measure when the cross has disappeared. We would use a light gate to measure how much light is passed through the conical flask. We would set the light gate to stop the timer at a certain light intensity, and the results we wrote down would be the time it took for the light to reach the given intensity with every different concentration. The computer measures it, so it automatically stops. This will help collect much more reliable evidence to support my conclusion. DIAGRAM OF LIGHT GATE We could use more accurate measuring instruments. The pipettes can be a lot more accurate, by using a longer, thinner pipette. We could also use longer, thinner measuring cylinder to measure out the water, Hydrochloric Acid and Sodium Thiosulphate in more accurate, larger quantities. To get more evidence for my conclusion, we could use a completely different reaction to see if my theory worked for that reaction. We could use: Mg + 2HCl MgCl2 + H2 From this reaction we could measure the amount of hydrogen released by the reaction, because in this reaction, the more hydrogen that is released, the faster the rate of reaction. To get more reliable evidence for my conclusion, we could use a data logger, which will measure the reaction time automatically, and gives no error in the place human error would occur. We could do the experiment for a lot longer or a lot shorter amount of time. We could use 10 Molar concentrations, and the reaction would be over in seconds, but the reading would be exact. We could also read 0.05 Molar concentrations, and the experiment would take hours, but the data logger could be left overnight and would log the time when it finished, whereas a human may miss it because of being tired or not being there. This means that wider gaps can be measured to make the evaluation and overall results more accurate, and will give a clearer pattern. 1 ...read more.

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