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How different variables will affect the rate of a reaction between Sodium Thiosulphate and Hydrochloric acid.

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INTRODUCTION: I am going to be investigating how different variable will affect the rate of a reaction between Sodium Thiosulphate and Hydrochloric acid. Sodium Thiosulphate + Hydrochloric acid Sodium Chloride + Sulphur dioxide + Sulphur + Water Na2S2O3 + 2HCl 2NaCl + SO2 + S + H2O Sodium Thiosulphate and Hydrochloric acid are both colourless solutions but when they are mixed together they become cloudy and eventually opaque. We can obviously not measure rate directly, but what we can measure is the time taken for a change to occur. Rate = Change/Time I will take the time by placing the beaker containing the Thiosulphate on a piece of paper with a cross on it. I would start the timing as soon as I added the Hydrochloric acid to the solution and I would stop as soon as I could see the cross no longer. For a reaction to take place two substances must collide. The rate of reaction depends on how many collisions occur in a given space for a given length of time. I will be measuring collisions/cm3/second. However not all collisions lead to a reaction because in order to react existing bonds must be broken - this needs energy, in a collision the kinetic energy of colliding particles might not be enough to break bonds. ...read more.


(ml) Time Taken (Minutes: Seconds) 0: 50 0:20 5: 45 0:24 10: 40 0:30 15: 35 0:29 20: 30 0:36 25: 25 0:56 30: 20 1:00 35: 15 1:40 40: 10 2:52 45: 5 6:20 50: 0 No Reaction From these results I can tell that having over 40 ml of water to 10ml of Sodium Thiosulphate is too much because it takes over five minutes to react and that is too long. So I have decided to only dilute the Thiosulphate to a ratio of 40:10 ml. I have also learnt that I should not include the results, which are under a minute. This is because my timing is far too inaccurate and any results under a minute are too close together. You can see this from my preliminary results where the timings go from 0:30 to 0:29 and then back up to 0:36 when it should continue to rise in a curve. I have decided to take the readings from 25:25 to 43:07, (Water : Sodium Thiosulphate) which is 8 readings. I have chosen to go no higher than 45:05 because of the reasons I explained earlier. It does not matter too much if my results are a bit under a minute because as long as it is over 40 seconds it should still be reliable. ...read more.


the same. My graphs look accurate if you look at them as an exponential curve but the end is still a bit erratic. If you look at the graphs there are no obviously anomalous results I can tell this because they are all in a close proximity to the line of best fit. The experiment was fairly easy to perform because the most difficult part was measuring out the amounts of the liquids accurately. I think I did this quite well however because if I had done it badly there would be a lot of anomalous results. I do not feel fully sure that my evidence is fully reliable because I think that I should have taken more results and I should have taken more time in planning my experiment and doing it with more care. Whereas what I actually did was to rush all of the planning and I was then forced to rush the experiment. I could improve it by using a wider range of concentrations, which would lead to a more accurate line of best fit. I would also have done each reading more than once and taken an average, which would have increased the accuracy. Possible problems with my coursework could have been the caused by human error. There could have been error in stopping the stopwatch, although this would have been minimal. ...read more.

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