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Investigate the rate of "Reactant" concentration on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid.

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Introduction

Year 11 Assessed Chemistry practical - SC1 - James Muir 11N Aim: To investigate the rate of "Reactant" concentration on the rate of reaction between Sodium Thiosulphate and Hydrochloric acid. The equation for which is shown below: Sodium + Hydrochloric --> Sulphur + Sodium + Sulphur + Water Thiosulphate Acid Chloride Dioxide The same equation is shown below, chemically and balanced respectively: Na2S203 + HCl --> S + NaCl + SO2 + H2O Na2S2O3 + 2HCl --> S + 2NaCl + SO2 + H2O My aim relative to the experiment is to investigate which chemical is used as the variable and how different concentrations of it affect the rate of time for a mark to become obscured. Variable under investigation: Either: 1) HCl - 2.0 Molar (stock) 2) Na2S2O3 - 0.15 Molar (stock) Variables: There are a variety of variables I can choose to measure when conducting the experiment. The most viable one, which relates to my aim, is by varying the concentrations of Sodium Thiosulphate and Hydrochloric acid, as this will provide me with the most relative set of results for the experiment. However I had considered other variables before beginning the experiment. These other variables were: 1) Temperature 2) Pressure 3) Particle Size 4) Light The problems with the above factors are always down to the equipment available and the complexity of the variables. For example temperature is a hard variable to study as it would need continual measuring. Likewise for variables such as Light, we would need specialist computer equipment which is not available for the experiment. Factors which affect rate of a chemical reaction: The rate of reaction depends on 4 things: 1) ...read more.

Middle

This indicates that there must be some relationship between Na2S2O3 and the time taken for the cross to disappear on the spotting tile. I do not need to draw graphs for these results as all the graph would show would be a straight horizontal line across the sheet. Preliminary background work: > Glassware - I chose to use beakers in my experiment in preference to conical flasks for a few simple reasons. Conical flasks have large bases and narrow necks, while beakers have a consistent shape and has the same depth throughout. Conical flasks are more awkward to stir and due to their inconsistent shape my cause different rates of reaction in some part of the flask due to different surface areas. > Stirring - this was necessary as it made sure the chemicals were mixed and the reaction was taking place under conditions of maximum efficiency. Prediction: I predict that varying the concentration of Sodium Thiosulphate will have a positive effect on the speed of the reaction. Hydrochloric acid has no effect on the rate of reaction as shown in my preliminary tests. I believe that when I vary the concentration of Sodium Thiosulphate the results will be inversely proportional to time due to the fact that it makes sense if results take less time when they react faster (inverse proportion). This means that as the concentration of Sodium Thiosulphate increases, the time for the black 'X' to obscure will be even less and less. This theory is backed up by my knowledge of the collision theory, explained below in my preliminary background work. I also believe my results to show that the inverse proportion of time to concentration theory will be proved - for example if I double ...read more.

Conclusion

I made sure that the apparatus I used was clean every time and that I was the only person making the judgements on when the mark became obscured in order to make the test fairer. To improve the accuracy of the concentration dilutions I could have used a burette or pipette as these allow a chemist to make more accurate solutions. It was also necessary to keep the stirring of the solution at a constant rate. No matter how steady your hand may be it is impossible to keep the same stirring speed throughout the experiment and prompts perhaps an ICT solution to replace a human stirrer. My results I gathered were both accurate and relevant. I was able to identify that hydrochloric acid was a useless variable to study after my preliminary tests and that I needed to use sodium thiosulphate. I collected and tabulated a set of results concisely, fairly and accurately, and this is proved on the graphs that I've drawn and the theory I've researched. This thus means that my conclusion is valid. I also needed to consider other variables to study in greater detail, and how they might increase other variables leading to increased reactions - for example temperature; is it true to say that an increase in rate might be down to temperature, and then a further increase of temperature causes an even increased reaction time? There is also the matter of the apparatus we used. In an ideal world we would use new, unused, perfectly clean and flawless glassware and measuring equipment. This however, is not feasibly possible and we were not using totally dry glassware for each test, which may lead to a false reading in our results - again something incredibly time-consuming to work around. By James Muir ...read more.

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