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To determine what affects the rate at which a reaction occurs between Hydrochloric acid and Sodium thiosulphate.

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Introduction

Introduction: The aim of this experiment is to determine what affects the rate at which a reaction occurs between Hydrochloric acid and Sodium thiosulphate. The reaction forms sulphur which is in the form of small solid particles which do not settle: they remain in suspension. I intend to find out whether varying the concentration has any effect on the rate of reaction between these chemicals. I believe that the concentration of Sodium thiosulphate has a direct affect on the rate at which the reaction occurs. Diagram of apparatus: Also, goggles will be worn. Procedure: * A cross will be marked on a little piece of paper. * I will dilute the Sodium thiosulphate by way of ratios. I will be measuring 50 cm of solution each time, with a measuring cylinder, but I will vary the volume of Sodium thiosulphate compared to the volume of water (from the tap) diluting it, making different concentrations of Sodium thiosulphate. I will use volumes of 50 cm of Sodium thiosulphate with no water, 40 cm of Sodium thiosulphate with 10 cm of water, 30 cm of Sodium thiosulphate with 20 cm of water and so on down to 10 cm of Sodium thiosulphate with 40 cm of water. ...read more.

Middle

* Cross: Different thickness, colours or sizes of the cross will provide me with unusual results. If a darker cross I used for another experiment then the time for the cross to disappear will obviously be longer because if it is very dark, then I will still be able to see it through the solution. * Distance of eye and angle of looking at conical flask: I might see the cross clearly at one angle/distance and not so clearly at other ones. * Chemicals from the same batch: The chemicals need to be from the same source over the period of days. But this will be difficult, co this could be a possible source of error. Also I will distinguish the recording of results from different days with a different coloured pen. The amount of substance doesn't affect the 'rate'. Even if different amounts are used, they will react at the same rate. Also the size of the container they are reacting in doesn't affect the chemical reaction itself, but it does affect the measurement of time, because the solution will be more spread out in larger containers so it will take longer for the cross to disappear because there is only a little height of solution between the cross and eye. ...read more.

Conclusion

Presentation of results: Treatment of results: To find a rate of reaction from the results I collect, I will divide 1 by the time in seconds (to make it inverse). This provides me with directly comparable rates of reaction, because as the time gets longer, the rate is much slower. The average results (inversed) will be used to plot a graph. I expect the graphs to look something like this: Measuring: I am going to use a 50 cm measuring cylinder to measure the amounts of water and Sodium thiosulphate and a 5 cm measuring cylinder to measure the amount of Hydrochloric acid. To be more accurate a drop pipette or a burette could be used but these methods a very time consuming. The time will be measure in seconds by a stopwatch. Preliminary work: I have done this experiment before varying the temperature instead of concentration. So that experiment has helped me make my predictions and also to plan out the experiment and procedure. I know what methods work and what to do, so I can get straight down to the experiment on the day. I can also check whether the range of my results are realistic or not. Secondary sources: * G..C.S.E Chemistry syllabus * Chemistry textbook- Key Science Eileen Ramsden * Internet- www.purchon.com/chemistry/rates.html ?? ?? ?? ?? G.C.S.E.- Chemistry Coursework Roshan Dandiker ...read more.

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