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The aim of this experiment is to determine what affects the rate at which a reaction occurs between sodium thiosulphate and hydrochloric acid.

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Introduction

Contents Plan * Aim (page 1) * Prediction (page 1) * Explanation (page 1) * Diagram (page 1) * Apparatus (page 2) * Method (page 2) * Measurements (page 2) * Fair test (including variables) (page 2) * Variables (page 2) - temperature of hydrochloric acid (page 3) - concentration of sodium thiosulphate (page 3) - size of conical flask (page 3) - catalyst (page 3) - cross (page 3) - volume of sodium thiosulphate and hydrochloric acid (page 3) - movement of reacting mixture (page 3) Observing * Safety (page 4) * Results (page 4) * First experiment results (page 4) * Second experiment results (page 4) * Third experiment results (page 4) Analysis * Evaluating results (page 5) * Experiment one line graph (page 6) * Experiment two line graph (page 7) * Experiment three line graph (page 8) * Average line graph (page 9) Evaluation * Conclusions (page 10) * Anomalous results (page 10) * Improvements (page 11) Aim The aim of this experiment is to determine what affects the rate at which a reaction occurs between sodium thiosulphate and hydrochloric acid. I intend to find out whether (and to what degree) varying the concentration of hydrochloric acid, has any effect on the rate of reaction between these chemicals. I believe that these variables are linked, and that the concentration of hydrochloric acid has a direct effect on the rate at which the reaction occurs. Seen as you cannot measure the surface area, the only two other possibilities of measuring the rate of reaction is the temperature or concentration. I chose concentration as it has more effect and is more precise. Prediction I think that as I increase the concentration of hydrochloric acid, provided that no other variables affect the results, the rate of reaction will also increase. Explanation I believe that this will happen because of the way in which the two chemicals react. ...read more.

Middle

This in turn could affect the results because if the cross is seen more easily, drawn with a thick marker, our measurement of how long the reaction took to complete would be longer and so the rate of reaction would seem slower. Equally, if the cross was hard to see, then it would disappear more quickly and the rate of reaction would seem quicker. I will keep this constant by using the same black pen to draw the cross each time, if I am unable to use the same cross each time, which is preferable, then I will do so. Volume Of Sodium Thiosulphate And Hydrochloric Acid - The larger the volume of hydrochloric acid and/or sodium thiosulphate, the greater total number of particles in the solution. This means that to completely react, and go cloudy, it will take longer. I will keep this variable constant by using 50cm� of sodium thiosulphate solution with 5cm� of hydrochloric acid each time. I have found from previous experiments that this volume (55cm�) is adequate because if too little is used then it is hard to see changes in it. Movement Of Reacting Mixture - If I shake the conical flask while it is reacting, then the reaction may speed up and therefore the rate of reaction would be quicker. Likewise, if I stir it then it will increase the rate of reaction. This is because there will be a greater chance of the particles colliding with other particles which they can react with because the two types of particles will be more mixed together and also, will have more kinetic energy because they will be moving while being stirred. I will prevent this from affecting the results by not stirring or shaking the mixture in any way. To make the experiment safe, I will be wearing goggles throughout, in case something unexpected occurs. I will be washing my hands regularly and thoroughly washing the equipment before each reaction to make sure that it is not only a fair test, but that it does not cause something dangerous to happen. ...read more.

Conclusion

However, I was later informed that, unfortunately, someone else in the class had mixed the two substances to form different concentrations in both bottles, therefore, in the third experiment, the trend was altered. I think that the only flaw in the experiment were in the measuring of the concentrations, and in the judging of when the reaction had completed of which corresponds to my actions. It was very hard to get an exact volume of water/hydrochloric acid to get the right concentration, and so this may have thrown the last result in the first experiment off the trend, too. Also, there was not really any sure way of knowing when the reaction had finished. My method of looking at the mixture and judging by the eye when the reaction is complete is very inaccurate, and leads to confusion, especially, for example, if you look away for a moment after thinking the reaction is over, and then look again and realise it hasn't. If I was to repeat the experiment, I would use a much more accurate way of measuring the volumes of the reactants, and I would find a completely different way of measuring when the reaction has completed. I think if I were to use an electronic device rather than the judgement of the naked eye then the experiment would be of far much more use and would conclude with highly accurate results. A laser may be appropriate as you could then see the particles moving and colliding but, unfortunately, I didn't have a resource of that kind. Also, I believe that with the use of a digital thermometer, I would keep track of the room temperature as that could also prove to alter the final results. Another possibility is to insure that you know exactly what you are doing by practising with a trial experiment first, of which I didn't do. I should have done this as I was perfectly equipped and able but I was under time restrictions and therefore, it was not possible for me to carry this out. C:\My Documents\coursework.doc\Kelly Duggan\NDO ...read more.

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