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To Investigate the Factors Controlling the Rate of the Sodium Thiosulphate with Hydrochloric Acid Reaction

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Introduction

To Investigate the Factors Controlling the Rate of the Sodium Thiosulphate with Hydrochloric Acid Reaction The Reaction: Na2S2O3 + 2HCl ? 2NaCl + SO2 + H2O + S This is easy to follow by observing the cloudiness produced by the sulphur. We will place the conical flask we are using over a printed black cross. When it is no longer possible to see the cross, the reaction is complete. Factors * Concentration of sodium thiosulphate * Concentration of hydrochloric acid * Temperature There is no catalyst in this reaction and surface area is not relevant as sodium thiosulphate and hydrochloric acid are miscible. Variable 1: Concentration of Sodium Thiosulphate I shall investigate the effect of changing the concentration of sodium thiosulphate. I shall keep the temperature constant (room temperature) and I shall use the same concentration of acid in each test. The reason we shall use room temperature is that it is the easiest temperature to regulate. I expect that increasing the concentration of sodium thiosulphate will increase the rate. I also expect that doubling the concentration of sodium thiosulphate will double the rate (halve the reaction time) i.e. rate ? concentration of sodium thiosulphate. This should be the case because the reaction can only occur if the sodium thiosulphate particles collide with the hydrochloric acid particles with enough energy to react. As the concentration of sodium thiosulphate is increased, there are more sodium thiosulphate particles present in the solution so there are more collisions per second. ...read more.

Middle

We then went on to get results for the other concentrations of sodium thiosulphate. Variable 2: Temperature I shall investigate the effect of changing the concentration of sodium thiosulphate. I shall keep the volume of the original solution of sodium thiosulphate constant (10 cm3) and I shall use the same concentration of acid in each test. The reason I shall keep the volume of the original solution of sodium thiosulphate at 10 cm3 is I need the times to be long enough to measure. I expect that if I increase the temperature I will increase the rate. I also expect that increasing the temperature by 10�C will double the rate (halve the reaction time). This should be the case because the reaction can only occur if the sodium thiosulphate particles collide with the hydrochloric acid particles with enough energy to react. As the temperature of the reaction is increased, the particles have more energy and so move about faster so there are more collisions per second. The major way that temperature affects the rate of reaction is by giving the particles more energy so that when they do collide they have more chance of colliding with enough force to react. This increases the number of successful collisions and so increases the rate of reaction. Keeping the concentration of the sodium thiosulphate solution constant is very constant is very important because the concentration has a big effect upon rate. ...read more.

Conclusion

As the concentration of sodium thiosulphate is increased, there are more sodium thiosulphate particles present in the solution so there are more collisions per second. This increases the number of successful collisions and so increases the rate of reaction. This conclusion supports both my predictions well. Evaluating This experiment seemed to work quite well to me. It was quite simple to conduct and it gave results that were easy to measure. From my graph, I can confidently state that I had no anomalous results. I think that one way we could have improved the procedure was to have taken five results for each concentration of sodium thiosulphate instead of three. This would have reduced the effect of anomalous results considerably. We could also have done the experiments in a thermostat. This way we could easily regulate the temperature accurately. Even if the dial were not set precisely on 20�C, (for example it may have been set at 21�C) all the experiments would have been conducted at the same temperature. Another way of improving the experiment would have been to shine a constant light through the conical flask and set up a light sensor at the other. Then we could set up a circuit so that when we start a timer it stops when there is no more light coming through the solution (it has turned opaque). This would give results that are more accurate and would give uniform times from student to student whereas when judging by eye people have different vision. ?? ?? ?? ?? Ahmed Luqman 1 ...read more.

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