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The Rate of Reaction between Hydrochloric Acid and Sodium Thiosulphate Solution

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The Rate of Reaction between Hydrochloric Acid and Sodium Thiosulphate Solution a) Introduction. When Hydrochloric acid is added to a solution of sodium thiosulphate, a reaction takes place in which sulphur is slowly precipitated and the mixture becomes more and more opaque. 2HCl (aq) + Na2S2O3 (aq) 2NaCl (aq) + H2O (l) + SO2 (g) + S (s) This gives us a simple way of finding the rate of reaction. If in each experiment, the same volume of solution is placed in a conical flask, then the depth of the solution will be the same for every experiment. If a cross were to be placed underneath the flask, the cross will disappear when the same amount of sulphur has been formed. If you measure the time it takes, the rate of reaction can easily be determined. Suppose that the mass of sulphur produced when the cross disappears is 1000 units and the time for it to disappear is 't', then, Rate = 1000/t In this investigation, the aim is to discover how the rate of reaction depends on the temperature of the solution. ...read more.


e) Method. * Add 20ml of Sodium thiosulphate to 30ml of distilled water in a conical flask. * Heat a water bath up to 25 C. * Add 5ml of Hydrochloric acid. * Start the stopwatch immediately. * As soon as the cross has disappeared, stop the watch and record the time taken. * To ensure a fair test, clean out the conical flask thoroughly with distilled water. * Repeat the experiment again * Repeat at temperatures of 30C, 35C, 40C, 45C, 50C, 55C and 60C, twice each so an average can be obtained. f) Results Temperature of water bath/ C Time taken for cross to disappear 1st time/s Time taken for cross to disappear 2nd Time/s Average time for cross to disappear Rate of Reaction/s Between sodium thiosulphate and Hydrochloric acid 25 65.01 56.50 60.76 1.64 30 42.66 39.94 41.30 2.42 35 34.50 34.12 34.31 2.91 40 25.25 24.66 24.96 4.01 45 19.18 18.34 18.76 5.33 50 16.09 16.69 16.39 6.10 55 13.12 12.88 13.00 7.69 60 11.12 10.87 11.00 9.09 From this table, a graph can be plotted, showing rate of reaction (x axis) ...read more.


This could not be proved as the reactions got too quick to record accurately. h) Evaluation The experiment is not perfect by any means but I would say there is definitely enough evidence to support a firm conclusion. On the graph, there is a very apparent best fit line, and the results backed up the conclusion very well. However, there are many points to be improved, and thought about. for one, the moment the cross has completely disappeared relies far too much on human judgement and is very dubious. When looking for something very intently, one may imagine something is there when it is not. Human reaction time on the stopwatch when this has registered on the stopwatch is also far from perfect, but this has to do without using severely complicated and expensive equipment. One problem with doing the experiment was the shortage of time. If we had considerably longer, then we could have used a much weaker concentration of sodium thiosulphate (say 10ml sodium thiosulphate and 40ml distilled water), thus being able to find out the rate of the reaction at higher temperatures, and perhaps discovering how high a temperature the reaction continues up to. Certainly, if further work on this topic was carried out, this would be the aim. ...read more.

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