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An experiment to investigate the effect of changing the concentration of Sodium Thiosulphate in the reaction between Hydrochloric Acid and Sodium Thiosulphate.

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An experiment to investigate the effect of changing the concentration of Sodium Thiosulphate in the reaction between Hydrochloric Acid and Sodium Thiosulphate. Introduction The reaction equation for this experiment is: Sodium Thiosulphate + Hydrochloric acid = Sodium chloride + Sulphur dioxide + Sulphur + water Plan Input variable: Concentration of Sodium Thiosulphate. 1) 5ml Sodium Thiosulphate 25ml water 2) 10ml Sodium Thiosulphate 20ml water 3) 15ml Sodium Thiosulphate 15ml water 4) 20ml Sodium Thiosulphate 10ml water 5) 25ml Sodium Thiosulphate 5ml water 6) 30ml Sodium Thiosulphate 0ml water I decided on these variables by doing trial runs on the experiment. Controlled Variables: a) Temperature b) Volume of Sodium Thiosulphate - water solution (always 30ml) c) Concentration of Hydrochloric Acid (always 20ml) d) Stirring (Y/N) Outcome Variable Time for Sodium Thiosulphate - Hydrochloric Acid - water solution to go cloudy. Experiment is considered over when a cross on a piece of paper cannot be seen by looking through the solution from above. Proposed Method a) I will set up the equipment - see below b) I will pour 20ml of Hydrochloric Acid into a measuring cylinder c) I will pour 30ml of Sodium Thiosulphate - water solution into a measuring cylinder. ...read more.


Trial Results Volume Hydrochloric Acid (ml) Volume Solution Sodium Thio (ml) Volume Water (ml) Time for solution to go cloudy (sec) Part One 20 5 15 151.8 20 7 13 132.6 20 5 15 148.8 20 10 10 95.4 Part Two 20 5 25 301.2 20 10 20 126.6 20 15 15 63.6 20 20 10 ---------------- 20 25 5 ---------------- 20 30 0 ---------------- I used my trial results to help me decide what values to use. Part one contains results that I decided not to use. 5 ml sodium and 15 ml water was an acceptable result but 7ml sodium and 13 ml water was not different enough to use those two as the range. 10 ml sodium and 10 ml water was different enough, but with 5 ml difference each time a total solution of 20 ml would not give me enough variables, e.g. only four. I then decided (see part two) that I would have 30 ml of solution with a range of 5 ml. This gave me a high enough range as well as enough variables (six). Results. Time for soln. to go cloudy Volume HCL (ml) Volume Sodium Thiosulphate (ml) ...read more.


Therefore, instead of only doing the 1st half I thought it would be more useful to repeat every other result to get a more accurate overall image. Appropriateness of equipment and procedure. I think that the equipment and procedure are both appropriate to the investigation, as they are safe, reliable and accurate. Improving the investigation. If I were to do the experiment again there are only two things I think I would change: * I would use a smaller volume of Hydrochloric Acid throughout, as this would allow me to repeat all of my results again. * I would also attempt to work slightly faster as this would give me time to finish all repeats. Both of these improvements aim not to improve the actual experiment , but just it's accuracy. Expanding the investigation How. I can only think of one way to improve the investigation and that is too do a similar experiment with just one change. Instead of concentration of Sodium Thiosulphate the controlled variable would be the temperature of the solution. Why. This would allow us to measure how temperature affects reaction rate, with the hypothesis being that the higher the temperature the higher the rate of reaction. If compared with the results of our investigation we could also see which affects the rate more out of these variables. ...read more.

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