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Investigating the effect of temperature on the reaction between Sodium Thiosulphate (Na2S2O3) and Hydrochloric Acid (HCl)

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Introduction

Investigating the effect of temperature on the reaction between Sodium Thiosulphate (Na2S2O3) and Hydrochloric Acid (HCl) Planning and Prediction Apparatus List Conical Flask 3 measuring cylinders Sodium Thiosulphate (Na2S2O3) Hydrochloric Acid (HCl) Thermometer Stop watch When sodium thiosulphate reacts with hydrochloric acid, the solution becomes opaque. I will investigate how the rate of this reaction is affected when the experiment is carried out at different temperatures. The reaction that occurs produces sulphur dioxide, water and sodium chloride. It can be shown by this equation: Na2S2O3 (aq) + 2HCl (aq) --> S (s) + SO2 (g) + H2O (l) + 2NaCl (aq) sodium thiosulphate + hydrochloric acid --> sulphur + sulphur dioxide + water + sodium chloride The rate of chemical reactions can be affected by a number of things: * changes in surface area * changes in concentration of the reactants * changes in temperature * added substances called catalysts * and changes in pressure if the reactants are gases. In most chemical reactions the rate changes with time, normally slowing down. Prediction I will be investigating the effect that temperature has on the reaction between sodium thiosulphate and hydrochloric acid. I predict that the higher the temperature, the faster the reaction will occur. ...read more.

Middle

This is because by the end of each experiment the temperature of the solution will have cooled and the temperature taken at the beginning would be inaccurate. Each experiment will be repeated at least twice and an average will be taken. This will ensure that results that are inaccurate will be noticed and the time will be as accurate as possible. The only variable in the experiment will be the temperature; the amounts of HCl, Na2S2O3, water and everything else will be kept constant. The apparatus must be carefully cleaned out after each experiment because just one drop of HCl in Na2S2O3 can contaminate it and make all the results inaccurate, as I found out in my preliminary tests. Results Desired Temperature (�C) Temperature at start (�C) Temperature at finish (�C) Time (seconds) 20 24 24 211 24 24 182 23 23 199 30 32 31 106 30 28 108 40 42 40 51 43 41 52 50 50 48 40 52 50 35 60 64 64 22 64 62 24 Averages Desired Temperature (�C) Average Temperature (�C) Average Time (seconds) Rate of reaction (1/time) 20 24 197 0.0051 30 30 107 0.0093 40 42 52 0.019 50 50 38 0.026 60 64 23 0.043 Conclusion As the temperature increases, the time for the cross to disappear decreases, so the reaction becomes faster. ...read more.

Conclusion

The first graph produced a good curve which did not seem to have any inaccuracies in the points. However, on the straight line graph the point for 60�C did not fit the straight line like the other points. It could be that the graph should curve up at this point. To see if this is the case I would have to take more readings, possibly at a higher temperature. The other, more likely, possibility is that the readings I took for 60�C were slightly inaccurate and although this did not show up on the first graph it showed on the second graph because the second graph used a much smaller scale. The rate of reaction appears to be too fast. It could be that the stopwatch was stopped a few degrees of a second out, or that the person watching the cross judged that the cross had disappeared too soon, or there could have been inaccuracies in the exact measurements of the sodium thiosulphate and the hydrochloric acid. Either way I would have to do further experiments to sort out the inaccuracy. To provide a more detailed pattern of results the experiments could be done at more temperatures, for instance every five degrees instead of every ten degrees like I did. My experiments showed quite successfully that temperature speeds up a chemical reaction at an increasing rate. ...read more.

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