Disappearing cross (aka Rate of reaction).
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Science Coursework Disappearing cross (aka Rate of reaction) Introduction This experiment is to investigate is two liquids, heated to an increasing temperature to see if it will make a reaction take place faster. The experiment I have used is the disappearing cross experiment, where two liquids, sodium thiosulphate and hydrochloric acid are mixed together and eventually the solution will become cloudy. I am going to investigate temperature in both of the liquids, heating them both to the optimum temperature before they are combined. The cross will be hand-drawn on paper and made water proof by covering it with sticky tape, due to it being underwater during the experiment. Once I have all the equipment in place I will mix the two liquids and measure the amount of time it takes for the solution to become cloudy. I will repeat this experiment 3 times to allow my results to be as accurate as possible. Each solution will have 10ml of sodium thiosulphate and 10ml of hydrochloric acid. The chemical reaction formula is: Na2S2O3 (aq) + 2HCL (aq) 2Nacl (aq) + H2O (l) + S (s) + SO2 (g). As a word equation that would be: Sodium Thiosulphate + Hydrochloric Acid Sodium Chloride + Water + Sulphur 4r2 + Sulphur Dioxide The sulphur created in the reaction is the precipitate. This precipitate is the solid and is what makes the solution so cloudy and makes the cross 'disappear'.
This shows that my prediction was almost correct, but the rate of reaction did not completely double each time the solution was increased by 100C. This can be due to errors in the experiment. To work out the rate of reaction I must divided 1 by the time that I had in my results table that shown how long the cross took to disappear. Rate of reaction This table show the rate of reaction of my experiments. 20 30 40 50 60 Test 1 0.06 0.08 0.14 0.3 0.5 Test 2 0.09 0.1 0.25 0.25 0.3 Test 3 0.09 0.1 0.2 0.2 0.3 Averages 0.08 0.09 0.19 0.25 0.39 From the table you can see that the rate of reaction when the temperature was 600C considerably faster than when the temperature was 200C. By looking at the results I can see that the prediction I gave that the reaction rate would be double for every 100C was not correct to my results. There are some exceptions though, the results that are in red, green or yellow are each pairs of the results that did correspond to my prediction and the collision theory. This shows that the theory is most likely correct, but the reason for so many results that were not double or nearly double for each 100C rise could have been due to human timing error. The other results are not completely opposite to the theory though.
Another possible reason why the result is anolumous is because different batches of the Sodium Thoisulphate and Hydrochloric Acid were used during the experiment due to the first batch being used up. The different batch could had been contaminated or a slightly different concentration and made the reaction work at a different rate. Even though one of the results is anolumonus I can take the results as reliable evidence because the results that were marked in the graph have an obvious trend. Further work The further work I could do it test the two liquids (1m Sodium Thoisulphate and 1m Hydrochloric Acid) at temperatures that I did not use. I can take both of the liquids to the lowest temperature possible before they both freeze. On the contrary I can use both the liquids at temperatures and test them before the temperature is so high they evaporate. This would give me a larger amount of results to put onto a graph and look for a larger trend than I have got, it would also allow me to see when the temperature get so high that the liquids cannot react any faster even if I make the temperature higher. I can also se the range from the coldest experiment to the hottest experiment. For further work I could take the results from the temperature in-between the temperatures I have taken. Ben Wilkins
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