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How does the Temperature affect the Rate of Reaction between Sodium Thiosulphate and Acid?

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Introduction

How does the Temperature affect the Rate of Reaction between Sodium Thiosulphate and Acid? PLANNING Introduction: We are investigating how the temperature affects the rate of reaction between Sodium thiosulphate and acid. This project will involve 4 parts, which in them will have separate sub-headings. We will be doing the planning, obtaining evidence, analysing and concluding and finally evaluating. All the different aspects of rates of reaction will also be taken into account. E.g. Other factors and how to make the test fair. The symbol equation for the reaction we are investigating is: Na2S203(aq) + 2HCL(aq) 2NaCl(aq) + H2O(l) + S(s) + SO2(g) The word equation for the reaction we are investigation is: Sodium thiosulphate + Hydrochloric acid Sodium Chloride + Water + Sulphur + Sulphur dioxide The rate of reaction can be found with the formula below: Reaction Rate = Change in amount of a substance Time Taken Theoretical Background: The rate of reaction can be calculated as with the equation shown above. When a reaction takes place it has to overcome a minimum energy barrier known as the Activation Energy. If the particles collide with less energy than the activation energy then nothing worth noting happens. "You won't get a reaction unless the particles collide with a certain minimum energy called the activation energy of the reaction." (Taken from www.chemguide.co.uk). Only those collisions, which have energies equal to or greater than the activation energy result in a reaction taking place. The reason why collisions have to overcome the activation is because every chemical reaction results in bond breaking. The activation energy is all about the breaking of the original bonds. So when the collisions between particles are relatively gentle there isn't enough energy available to start the process of breaking bonds and there the particles do not take part in a reaction. If the particles collide with less energy than the activation energy they simply bounce apart. ...read more.

Middle

For example stirring affects the rate. The way in which we will control these factors is to keep them constant. There are also many variables that will be measured and kept the same or changed. By breaking them down it is easier for us to follow: Variable changed: * Temperature Variable measured: * Time taken for Rate of Reaction Variables kept the same: * Volume of sodium thiosulphate * Volume of acid * Concentration of acid * Concentration of sodium thiosulphate * Cross on the paper By changing any one of the variables that we kept the same would mean that our results would become very inaccurate. For example if we changed the cross on the paper, it might affect the time we see it disappear because a bright red cross might stay visible to us for a longer period of time than a pencil cross. Also the stirring will have to be consistent as different rates of stirring will mean a change in the rate due to particles moving faster or slower depending on the speed at which the solution will be stirred. Another point to make about a fair test is that a Bunsen burner is not good for maintaining a constant temperature whilst we heat the solution up. Whilst heating the solution, the water in the solution could evaporate in the duration of time it takes for the Bunsen to heat up the solution to our desired temperature. This means that the concentration of the solution will be affected. The temperature ranges were from 20oC at 10oC intervals all the way until 60oC. There is another point to think about when deciding how to set up the apparatus, where to put the paper with the cross. If it is put underneath the beaker and on top of the gauze it will get burnt so the ideal place to put it is out of the way and the best thing to do is move the beaker on top of the paper. ...read more.

Conclusion

Therefore we will not have to take the average temperature or initial and final and this would make collecting the results easier and our target temperature can then easily be reached. 3) Evaporation of solution at 60oC. This increases the concentration and therefore affects the rate. There is no real way to escape this problem. However a closed system could be used to stop any vapour escaping but the experiment has to have an outlet. I would personally close the beaker by putting something over it as I believe this would be a good place to start to get rid of this problem 4) Judgement of the cross disappearing. This could make our results inaccurate as the disappearance of the cross is vital and 2 seconds out could cause an anomaly. Also we can't judge the disappearance to a 100th of a second. A light sensor attached to a LogIt can be used to judge the disappearance of the cross at the precise moment. This will increase the accuracy of our results. 5) Hydrochloric Acid - When we added the hydrochloric acid into the heated solution of water and Sodium Thiosulphate there would have been a temperature change because the hydrochloric acid wasn't heated and therefore cold acid was added to a warm solution. Using a water bath would control this factor. 6) Whether or not the reaction was exothermic or endothermic. Using a thermostat controlled water bath would make sure that if the temperature dropped too low or too high Validity and Reliability: Validity - Whether or not the results answer the main title. If I had more time to carry out the experiment I would increase the validity by increasing the temperature range and also improving the experiment with the improvements above. I would increase the reliability by just repeating the experiments more than once. The more times you carry something out the more reliable the evidence becomes. Further Work: Another experiment that could be carried out to extend and improve the work that I have done is shown below. ...read more.

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