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'How does the concentration of Sodium thiosulphate solution affect the rate of its reaction with hydrochloric acid?'

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Introduction

'How does the concentration of Sodium thiosulphate solution affect the rate of its reaction with hydrochloric acid?' The aim of my experiment is to investigate how the concentration of Sodium thiosulphate solution affects the rate of its reaction with hydrochloric acid. I am going add water to the sodium thiosulphate solution to weaken the concentration so I can see how it can affect the rate of reaction. I shall add water as that is the only way I can find out how concentration affects the rate of reaction as I cannot increase concentration from 1M upwards as I do not have the resources available to use. Prediction I predict that when I add more water to the sodium thiosulphate solution, the time it takes for the dot on the beaker to disappear will lengthen. I predict this because, for particles to react they must collide with each other. If there is a higher concentration of sodium thiosulphate particles in a given volume there is a higher chance of the particles colliding together succesfully and reacting. This is because they are so close together. If you weaken the solution, (so there is a much lower concentration of sodium thiosulphate particles to react with the hydrochloric acid,) then there is less chance of the particles colliding succesfully and reacting as there are less particles in the given volume, so the reaction time will slowly lengthen as the concentration goes down. ...read more.

Middle

Volume of water (cm3) Concentration of Sodium Thiosulphate (mol/dm3) Time taken for dot to disappear (s) Rate of Reaction 1/t ( /s) 10 0 1 5 0.2 8.5 1.5 0.85 7 0.142857142 7 3 0.7 9 0.111111111 5.5 4.5 0.55 10 0.1 4 6 0.4 15 0.066666666 2.5 7.5 0.25 21 0.047619047 1 9 0.1 35 0.028571428 Conclusion I discovered that there was not enough variation in the concentrations. So I decided to change the concentrations I was going to use. I found out that doing seven concentrations was enough as it . I also did not make the tests accurate enough as I do not have a big enough range to draw many conclusions. From these results, they look like they back up my prediction, as the time for the dot to disappear lengthens as the concentration of the Sodium Thiosulphate goes down. I shall now vary the volumes of the water and Sodium Thiosulphate by 5cm3. An example of this would be having 45cm3 of Sodium Thiosulphate and having 5cm3 of water, then 40cm3 of Sodium Thiosulphate and 10cm3 of water. This then would carry on going up or down in either direction as needed, this will give me extra accuracy. Final Experiment Volume of Sodium Thiosulphate Solution (cm3) Volume of Water (cm3) Concentration of Sodium Thiosulphate (mol/dm3) ...read more.

Conclusion

Therefore I think if I repeated this experiment I would repeat the variations at least 4 or 5 times rarther than three times, if I did then my results would be a lot more accurate. Apart from that point I think that I did discover enough information to help me lead to a conclusion. If I would do the experiment again I would use a light sensor to detect whether or not it could see the light through the cloudy reaction. This would mean that the experiment would be more accurate. Also using the same equipment may have a small effect on the results, or cleaning the flasks out after each experiment may help. Another improvement could be to use a water bath to keep the temperature of the reaction the same throughout, as it would not then be affected by the heat from the classroom. I would also do the whole experiment, including the repeats on the same day so no variations can occur because of different days. To obtain more evidence to support my conclusion I would take more of a range of results. I might use more concentrated Sodium Thiosulphate or use less concentrated Sodium Thiosulphate. More evidence would mean that there would be more verification that my prediction was correct, and would solidify the concept of the collision theory. Overall I think I have done an interesting investigation, and have completed it to the extent of my abilities. I have tried to make it a fair test, and back everything up with solid evidence. ...read more.

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