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Investigating how concentration affects rate of reaction

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Lindsay Newell Investigating how concentration affects rate of reaction Planning Introduction The experiment I am doing to change the rate of reaction is: Sodium thiosulphate + Hydrochloric Acid � Sulphur + Sodium Chloride +Sulphur Dioxide + Water Na2S2O3 (aq) + 2HCl (aq) � S (s) + 2NaCl (aq) + SO2 (g) + H2O (l) Possible ways of changing the reaction time are: * Changing the concentration, if you increase the concentration there will be more collisions because there are more particles in the same volume, * Changing the temperature, if you increase the temperature it will make reactant particles move faster and collide more often, * If a catalyst is present, it will speed up the reaction. I will be changing the concentration because it is the most suitable thing to do. Aim For this experiment I am changing the concentration of Sodium thiosulpate to alter the reaction time for the reaction between sodium thiosulphate and hydrochloric acid. Hypothesis I am going to change the concentration of sodium thiosulphate by adding water to it. By doing this it should take longer for the mixture to go cloudy. Fair test To make my test fair I will have to make sure: * The concentration and volume of hydrochloric acid stays constant, * The outside temperature is constant, because if it is too hot and heats up my experiment the particles in the chemicals will move faster making them collide more often. ...read more.


Concentration of Sodium thiosulphate when water is added (g/dm�) Time taken Temperature (�C) 40 30.28 sec 26 35 35.25 sec - 30 44.47 sec - 25 51.94 sec 26 20 1 min 3.53 sec - 15 1 min 34.93 sec - 10 2 min 35.29 sec - 5 6 min 16.09 sec 26 In my preliminary I did what I described in my method and used all of the volumes and concentrations I stated, I think my preliminary test went very well although there are a few things I will do to retrieve exact results. When I did the preliminary I found what I guessed in my prediction and what I will be able to explain in more detail after my real experiment, but I found that the lower the concentration of sodium thiosulphate the longer the time. With my preliminary results I came across a few problems, the cross on the paper got wet and the cross faded every time I repeated the experiment. To fix this I could: make photocopies of the same cross for every repeat, wipe the bottom of the flask dry after each time I rinse it out and be careful when pouring chemicals or I could draw an "X" and have it laminated. I think I will just wipe the bottom of the flask each time as if I photocopy the "X" the machine could be running low on ink and make the second "X" fainter then the first. ...read more.


the inside to make sure the excess water did not affect the experiment, I noted down the size of all the beakers and measuring cylinders as well. If I had used a different sized beaker it would have made a large difference, say I had used a larger beaker instead that would men that the chemicals would be more spread out so the reaction would take place and the cross would have taken longer to disappear. The opposite would happen with a smaller beaker. I did not get anomalous results because the graph was a curve. I chose to use a curve because it looks better and the results would not fit a line of best fit. The only thing I will say about my curve it there is quite a large gap between the points at 30 and 35. This could be because there is suddenly not a lot of sodium thiosulphate to react with the hydrochloric acid. It also could have been because of a mistake I made, but it happened in every experiment I did including the preliminary. Further work to do on the experiment would be to research a wider variety for results and compare them with what I have already done or test another way of altering the reaction time of sodium thiosulphate and hydrochloric acid. By doing this I could see if it is quicker to do it by changing the concentration or the new method, and I could also see which one was more accurate. ...read more.

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