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Experiment to find the relationship between the concentration of Sodium Thiosulphate and the rate which it reacts with Hydrochloric acid.

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Introduction

Experiment to find the relationship between the concentration of Sodium Thiosulphate and the rate which it reacts with Hydrochloric acid. Introduction The rate of reaction is measured by finding the quantity of product made in a certain time. The rate of reaction can be made faster by an increase of temperature, adding a catalyst, increasing concentration or pressure or making the reactants surface area larger. An increase in temperature causes the particles of the reactants to gain more energy and move faster. Collision theory states that this results in more collisions and more of these collisions will have enough energy to cause a reaction. By adding a catalyst the particles will stick to the sides of the catalyst and this increases the rate of reaction. By increasing the surface area there is more surface for the particles to collide with thus causing more collisions and increasing the rate of reaction. Finally by increasing concentration there are more particles moving around in the same space. This equals more reactions, which equals faster rate of reaction. More collisions = faster rate of reaction. In this experiment I shall be investigating the relationship between the concentration of sodium thiosulphate and the rate of its reaction with Hydrochloric acid. The formula for this reaction is: Hydrochloric acid + Sodium thiosulphate >>>>>>> Sodium chloride + Sulphur oxide + Sulphur + water 2HCL(aq)+Na2S2O3(aq)>>>>>>>>>>>>NaCl(aq)+SO2(g)+S(s)+H2O(l) ...read more.

Middle

Result 2 Time (s) Result 3 Time (s) Mean average of results (s) 1 2 3 4 5 As you can see the average will be taken from three returned results. This increases the reliability of the results. Anomalous readings can be easily spotted and commented upon. We have chosen five different concentrations for a greater spread of readings. This makes it easier to evaluate the results and come to a conclusion. To make the test fair all other variables such as temperature will be kept constant, the same person will observe the reaction each time, the total volume in the conical flask will be kept the same and 5cm cubed of the same HCl will be used each time. We have to remember though that some variables (such as temperature) are very hard to continuously control but dramatic changes are not expected. Inaccuracies may possibly be caused by the limitations of humans and equipment during measuring and in making the judgement that the cross is no longer visible. The mean averaging of the results combats this. To ensure our safety goggles and aprons are always worn to protect the eyes and body. Results Experiment Concentration Result 1 (in seconds) Result 2 (in seconds) Result 3 (in seconds) Mean average of results (s) Rounded mean average (s) 1 40g per litre 37.9 42.09 30.58 36.86 37 2 36g per litre 45.5 43.25 48.68 45.81 46 3 32g per litre 45.37 48.28 51.72 48.46 48 4 28g per litre 48.53 60.38 55.6 54.84 55 5 24g per litre 70.94 76.15 79.09 (42.9) ...read more.

Conclusion

There were a few anomalous results, the most obvious being the 42.9 seconds that was found in the last experiment. We believe that this was caused by an amount of leftover HCl being left in the conical flask and speeding the reaction up. We decided to leave this result out of the final mean value and the graphs. The other possibly anomalous result is the final mean result of the 5th experiment. If you look at the rounded mean result in seconds graph you can see that the line of best fit does not go near this mean result of 75 seconds. This is probably because of the lower ambient temperature on the day that we did this experiment that caused a slower rate of reaction and so increased the time taken for the experiment to finish. . If I did the experiment again I would try to do all the experiments in the same day. This would make the ambient temperature more constant and therefore the temperature would affect the results equally. Another possible source of error was difficulty in judging when the cross disappeared. Possibly we could measure the rate of reaction by collecting the sulphur dioxide produced. Overall, however, we followed the stated method for each of the experiments and I believe that it went quite well and it gave a good set of results that display the predicted pattern for this experiment. It supports my conclusion because it shows that the time taken for the experiment to finish is inversely proportional to the concentration of Sodium Thiosulphate. ...read more.

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