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Investigating the kinetics of reaction between sodium thiosulphate and dilute hydrochloric acid.

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Chemistry Coursework Investigating the kinetics of reaction between sodium thiosulphate and dilute hydrochloric acid. Introduction: The reaction to be studied is as follows: Na2S2O3 + 2HCl 2NaCl + H2O + SO2 + S There are several possible ways of finding out the reaction rate, as there are four by-products formed in the above reaction. The fact that sodium chloride is in solution accounts for why it is not suitable to be collected. Water is hard to measure, as there are too many moles of it in comparison to the salt, which is in aqueous solution. Sulphur dioxide gas would be a suitable factor for measuring reaction rate, and it would not have to separated from any other gases, as no other gases are given off. However, it will react and dissolve into the water, and it is also fairly toxic, making it a safety hazard. This leaves us with sulphur, which is left as a solid. Sulphur is the most suitable substance to measure reaction rate, as when the two colourless, aqueous solutions are mixed together, a cloudy precipitate is formed. This is the sulphur, which is insoluble in water. Therefore, an experiment can be designed to measure the amount of time for the solution to completely precipitate. ...read more.


To discover reaction rate, we need to know when the solutions have completely precipitated. In this case, we can put a piece of paper, with an X, under a conical flask and see how long it takes for the X to disappear from view, because of the precipitate formed. The experiment was only a rough guide, so only the maximum and the minimum concentrations were tested, to ensure that the experiment worked as it was supposed to. This was then repeated to back up the original, and make sure that there were no extremes. The results are as follows (all volumes are in cm3): Acid Volume Na2S2O3 Volume Water Volume Time taken (s) 1 2 10 50 0 38.78 36.47 10 10 40 186.03 189.75 Main Experiment Apparatus: 1 piece of paper 1 marker pen 2 large beakers (500ml) 1 measuring cylinder (100ml) 1 measuring cylinder (25ml) 1 conical flask 1 pipette 1 distilled water bottle 1 stop watch 2 thermometers Sodium Thiosulphate Dilute Hydrochloric Acid Method: 1) Take a piece of paper, and using the marker pen, draw a large X onto it 2) Put the thermometers into the two solutions, to ensure that the same temperature is maintained throughout the investigation. ...read more.


From the graph, we can see that the rate:concentration graph is almost a straight line, which is as predicted. Evaluation: The set of results which I obtained was quite reliable, as it agrees with my hypothesis, which was made using detailed scientific knowledge. And also, there were three sets of results taken, all of which are relatively close to the average. The stopwatch records milliseconds, but for a person to acknowledge the change of colour and stop the clock, makes results a little bit inaccurate. Also, the extent of the reaction, although seen by the same person and through the same eye(s), it is hard for the eye(s) to notice the exact point at which the colour changes on 15 separate occasions. Therefore, as an improvement, I would use a colorimeter to measure the extent of the reaction. And, if possible, I would attach this to a stopwatch, so that the when the reaction was sufficiently complete, the clock would stop. I am not surprised that my graph for rate against time is not a perfect straight line, as with any experiment, there is a certain amount of error, which cannot be abstained. The results for 14.8 g/dm3 and 22.2 g/dm3 are a little odd, but still show the growing trend. I would repeat these results again, if possible. ...read more.

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