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Investigate the principal factors that affect the rate of reaction between Sodium Thiosulphate and hydrochloric acid.

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Introduction

Rates Of Reaction Coursework Aim: To investigate the principal factors that affect the rate of reaction between Sodium Thiosulphate and hydrochloric acid. Theory: The reaction between sodium thiosulphate solution and dilute hydrochloric acid: HCl+sodium thiosulphatesodium chloride+sulphur dioxide+sulphur+water. HCl(aq) + Na2S2O3(aq) NaCl(aq) + SO2(g) + S(s) + H2O(l) The sulphur formed in this reaction makes the colourless solution go cloudy. The reaction is usually carried out in a flask placed on a piece of white paper which has a black cross on it. At the beginning of the reaction, the cross can be seen easily. As the flask becomes more and more cloudy, the cross gets harder to see. Factors which affect the rate of reaction: * Increasing the temperature of a reaction increases the rate of a reaction. At the higher temperatures reactant particles move faster and collide more often and more violently. For every 10?c rise in temperature, the rate of reaction doubles. * Increasing the concentration of reactants increases the rate of a reaction. This is because there are more particles in the same volume so more collisions are possible every second. ...read more.

Middle

Although my results did not completely satisfy this statement, there is some evidence to prove it. At high temperatures, the rate of reaction is very rapid; therefore the time for the reaction to take place is quite small. If you lowered the temperature by 10?c you would expect the time for the reaction to double (20 secs for 50?c, 40 secs for 40?c). My results were very similar to these model results but not always exact. The theory that the rate of reaction doubles for every 10?c rise in temperature always gives a curved graph, it will never be a straight line. My graphs for temperature versus time show this very well. My other prediction was that increasing the concentration of the reactants would increase the rate of reaction. My results agree with this prediction. Concentrated sodium thiosulphate reacted a lot faster than dilute sodium thiosulphate. The results go down fairly steadily on the graph but the 25cm? result could be an anomalous result. This result could be correct. The line of best fit is wrong as it says that the solution will go cloudy in 209 seconds when there is no sodium thiosulphate present. ...read more.

Conclusion

This caused a drop in temperature when the sodium thiosulphate and acid were mixed. This is not important as it is a systematic error (it happened every time and made the temperature drop by the same amount). This could explain the reason why the rate of reaction did not always double for every 10?c rise in temperature. The beakers used were washed before each experiment. There was no chance of contamination from other chemicals as they were all washed with sodium thiosulphate before hand. Future Investigations/Improvements: If I could do the experiment again, I would make a few changes. These changes would give more accurate and also a wider range of results. I would use a magnetic stirrer as opposed to hand if possible. The magnetic stirrer can be set to a certain speed and remains at that speed for the whole experiment. I would use light sensors to decide exactly when the reaction had reached the completion point, as they are far more accurate than the eye. I would repeat each experiment at least 3 times to ensure that the results are accurate. I would heat the acid as well as the sodium thiosulphate when investigating temperature. This would mean that the acid wouldn't cool down or heat up the solution. ...read more.

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