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Investigating the rate of reaction between Hydrochloric acid and Sodium Thiosulphate by varying the concentration of the Thiosulphate.

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Introduction

Investigating the rate of reaction between Hydrochloric acid and Sodium Thiosulphate by varying the concentration of the Thiosulphate. Aim: I will be investigating the reaction between hydrochloric acid and sodium thiosulphate. In order to determine if increasing the concentration of sodium thiosulphate has an affect on the rate of reaction. I will do this by keeping the volume and concentration of hydrochloric acid constant throughout the experiment. However I will be changing the concentration of sodium thiosulphate by diluting each trial with distilled water. This will result in the sodium thiosulphate decreasing in concentration but its volume will remain the same. By reacting these substances and timing how long it takes for sulphur to be formed (which causes the solution to go cloudy), I will be able to time the reaction and from this calculate the rate of reaction. Prediction: I predict that as the concentration of sodium thiosulphate is increased the faster the rate of reaction. Hydrochloric acid and sodium thiosulphate are both clear and therefore are see through. On adding the two substances together a reaction will occur to produce sulphur. Subsequently the solution will go cloudy (due to the formation of sulphur) obscuring the view of the cross on the tile. As the concentration of a substance is increased the number of particles per dm3 also increases. This means that there are more particles present in the same volume and therefore more collisions will occur in a given period of time and thus the rate of reaction will be faster. In this reaction between sodium thiosulphate and hydrochloric acid, increasing the concentration of sodium thiosulphate means that the black cross on the tile will disappear in ...read more.

Middle

Due to the solution becoming cloudy I was not able to see the black 'X' on the tile, when I could no longer see it I stopped timing on my stop watch, this told me that the reaction between the sodium thiosulphate and hydrochloric acid had come to an end. I repeated the same procedure with the hydrochloric acid and sodium thiosulphate but instead used different amounts of each substance. I did three other experiments including: * 25 ml of sodium thiosulphate reacting with 5ml of 2 mole hydrochloric acid * 40 ml of sodium thiosulphate reacting with 5ml of 1 mole hydrochloric acid * 40 ml of sodium thiosulphate reacting with 5ml of 2 mole hydrochloric acid Results: Volume of Sodium Thiosulphate (ml) Volume of Hydrochloric acid (ml) Molarity of Hydrochloric acid Time taken for reaction to occur (seconds to 2 d.p.) 25 5 1 65.18 25 5 2 52.73 40 5 1 42.61 40 5 2 33.97 Conclusion: From my results I am able to see what measurements for each substance I am going to be taking for my final experiment. I have decided to use 40 ml of sodium thiosulphate. I have decided to use 40ml of sodium thiosulphate because it gives me a better variety of results and would provide me with a better graph, also when conducting the 25ml of sodium thiosulphate experiment I found that it took too long to react with the hydrochloric acid and this would not be the best way to manage my time. I found the volume of acid used to be sufficient for a reaction to occur. ...read more.

Conclusion

The improvements that could have been made to this experiment were keeping the temperature at which the experiment was being conducted more accurate. This was because the room temperature was not as reliable and it fluctuated consistently throughout the time in which the experiment was being conducted due to windows and doors being opened and closed throughout the experiment. New conical flasks should have been used as a residue amount of hydrochloric acid and sodium thiosulphate may have remained in the flask and could have affected the results. I think that the point at which the cross disappeared was a controversial issue as a persons judgement is different every time, a data logger could have been used to eliminate this problem it could have been attached to a computer and should have been light sensitive to tell when the cross on the tile had disappeared. If I were to repeat this experiment again, I would use a more accurate way in telling me when the experiment was over e.g. by using a light sensitive data logger, I would also use clean conical flasks or wash them out more thoroughly to help gain more accurate results. From my results I produced a graph which showed me that I had no anomalous results as all the plotted points fitted into the graph accurately and also the figures obtained in my data seemed to resemble each other. Further experimentation I would test the other factors that affect the rate of reaction for example temperature, surface area and the use of a catalyst. Omar Jamshad 10S / B1 ...read more.

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