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I am going to investigate the factors that affect the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

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Key Stage 4? Science 1 Assessment Investigating Rate of Reaction Plan I am going to investigate the factors that affect the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid. These two react together according to the equation bellow: Sodium?????????????????Hydrochloric?????????????Sodium????????Water?????Sulphur? Thiosulphate?????????????Acid???????????????????????Chloride??????????????????????Dioxide? ??????????????????????????????Sulphur ???a?S???????Cl?????????????????aCl?????????S?????S The factors which I could investigate and that have an effect on the rate of reaction are volumes of solutions, density, temperature, concentration, the way in which you are going to view and record the rate of reaction i.e. from what angle/side and the last factor which would affect reaction is different ways of stirring the solution. The factor, which I will choose to change, is the concentration of solution. To help me carry out my main experiment, I am going to base it on my preliminary experiment. From the results of my previous experiment, I can make a prediction fro the one I'm doing now. On my preliminary I did five readings and that worked fine, but I thought that if I did it six times, I would have had a more accurate reading. Each time I was either increasing or decreasing the factors by 5, so this time I will do the same again because I think that worked. Having chosen the factor I am going to predict that as the concentration Sodium Thiosulphate increases, the time taken for the reaction decreases, which means that rate of reaction increases. I think this was because the increase in molarities means more solute in the same amount of solvent. ...read more.


because the mixture wasn't as diluted and a lot slower by the end of it, when most of the mixture was water which is very un-reactive. Conclusion From the graph it can be seen that as the volume of Sodium Thiosulphate decreases i.e. the concentration of Na S O decreases, the time taken for the reaction increases, which means that the rate of reaction decreases. My prediction was correct as this is exactly what I said would happen, because as we increased molarities we increased the collision effect and the rate of reaction with it. Now since rate of reaction is amount of sulphur produced divided by time then, if the amount of sulphur stays the same i.e. enough to produce the colour change then the rate of reaction can be judged by taking values of 1/time. Since the amount of sulphur is same in each experiment ( i.e. the amount needed to make a clear colour to cloudy) then Rate of Reaction = Constant / Time Taken Rate of reaction is proportional to the recepireal of the time taken. Therefore a graph can be drawn of rate of reaction (1/time taken) against concentration ( judged by volume of Sodium Thiosulphate). Concentration of Volume of Na S O Sodium Thiosulphate Total Volume of Solution Total volume is always 40 cm , so it has a constant volume. Therefore concentration of Sodium Thiosulphate is the volume of Na S O Constant So concentration of Sodium Thiosluphate is proportional to the volume of Sodium Thiosulphate. ...read more.


This time I will stir the solution a bit and with constant strength. I will also keep the concentration of solution the same. The only thing that I will be changing this time is the temperature. In this experiment I am going to observe the colour change when all the reactants have been added together and note down the rate of reaction. I will make only 5 measurements this time, because 6 didn't really make much difference. First I will get all solutions ready and set up the apparatus. This time I will need a Bunsen burner as well as tripod and safety mat. I will measure the starting temperature and then add on 5� with each run. The first run I will do without heating up the mixture because it will be at room temperature, but then I will heat it up and will have thermometer in the conical flask so that I will be able to tell when it reached the next set temperature. I will have the cross on the side of the flask away from the fire, so that it doesn't go up in flames ( safety precaution). Last time the cross was underneath the flask but it can't be this time. I am going to wait for the mixture to go opaque. I will start the stop - clock as soon as I put the last drops of everything in and the temperature is at what it should be. When I have obtained all of my results I will then plot them on the graph. This is now the plan of the experiment which would provide additional relevant evidence towards my conclusion. Diana Rough 11L1 ...read more.

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