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Chemistry Coursework - How the concentration effects the rate of reaction between sodium thiosulphate and hydrochloric acid.

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Introduction

+Chemistry Coursework-How the concentration effects the rate of reaction between sodium thiosulphate and hydrochloric acid By Jess McFarlane 11WM Introduction Sodium thiosulphate and hydrochloric acid are two colourless solutions that gradually react together to form a cloudy yellow precipitate of sulphur when they are mixed. I am looking to record the rate of reaction, which is measured by dividing 1 by the time taken for the reaction to occur, (1/time taken). I have chosen to vary the concentration because it is more practical to investigate, as it would take longer to prepare if I varied the temperature of the reactants and also it is much more difficult to obtain a desired temperature of a reactant, which will produce less accurate results. The chemical equation for this experiment should look like this: HCl + sodium thiosulphate sodium chloride + sulphur dioxide + sulphur + water. 2HCl (aq) + Na2S2O3 (aq) 2NaCl (aq) + SO2 (g) + S (s) + H2O (l) My aim is to do this experiment but vary the concentration of the sodium thiosulphate so that it will affect the rate of reaction and I can then record and see why this reaction occurs. There are a few factors that could affect my experiment and the rate of reaction and so they need to be kept constant in order for my experiment to work. The collision theory states that reacting particles factors, which will affect the rate of a reaction. And the main two in this experiment the temperature, and the concentration of the solution. Prediction First of all I predict that as the concentration of the sodium thiosulphate increases, the rate of reaction will be faster and therefore make the X on the card under the conical flask disappear quicker. This is due to the effect of the collision theory. As the concentration is higher this means that there are mare sodium thiosulphate molecules to react with HCl molecules. ...read more.

Middle

Once these set of results are collected and the equipment has been thoroughly washed through, I will repeat the experiment in aid for my evaluation and conclusion. To make this a fair test I must keep a lot of the variables constant. This means that I must keep the following the same as possible otherwise they could interfere with my set of data: 1. Temperature 2. Volume of Hydrochloric acid 3. Total volume of all the solutions together The temperature will have to be constant throughout the experiment so that the rate of reaction is not affected. This is because if the temperature rises in any way, the particles will gain more heat energy, which is converted into kinetic energy. This makes the particles move around faster, resulting in more useful collisions, which in turn increases the rate of the reaction and therefore making the experiment unfair. I will not actually be able to keep it constant but I must try my best in keeping everything the same to ensure that a fair test will be made. I will then have to keep the HCl constant as if I were to change this, it would have a vast effect on the rate of reaction, increasing it if there was too much HCl and decreasing the rate of reaction if too little was added. This would obviously play quite a serious part in the experimental error side and therefore should be measured as accurately as possible. Also to ensure the test is fair, the variables will have to be done at a fair and precise rate. And what I mean by this is how they should be measured accurately in both tests so that no experimental error could occur because due to these side effects the whole experiment could be affected. The rate of reaction could seriously be affected by what seems such an insignificant piece of data error. ...read more.

Conclusion

And when I say this I mean that the levels should be accurate every time otherwise this may cause some experimental error and may be a factor of concern when collecting the data. I did though in fact record the solutions as precisely as I could and under the supervision of my partner whilst carrying out the experiment. There is also the factor of the stopwatch. Even though the recordings were accurate, the stopwatch may not provide a piece of suitable time keeping equipment as it could be slow or the persons reactions who is keeping the time could not be too fast but once again this would raise any major concerns in the investigation. I have also come up with another way in which I could improve my experiment. My background knowledge on this particular part is not to good but instead of using my own personal eyes so that I can time how long it takes for the cross (as explained before) to disappear underneath the conical flask, I would use a photo electric cell and a light sensor. It is a rather basic process of where I would place the light sensor underneath the conical flask instead of the X and set the photo electric cell above the conical flak. The idea is, as soon as the light sensor is unable to sense anymore light that the cell emits it, hence the solution has reached it's full potential, we are informed. So I would turn on the cell and stopwatch together and as soon as the light sensor would be unable to fulfil it's deed and alarm me I would turn the stopwatch off. This is a much more precise way of getting a reading and would cut any experimental error out when dealing with the time factors. But it is not possible all the time to receive such high tech equipment and the facility was not available for use for the whole class. The diagram below represents this second method. 1 ...read more.

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Here's what a teacher thought of this essay


This is a detailed experiment, however the author repeats themselves many times throughout. It is not set out very well and has no diagrams or graphs to view.

The science is sound, but very basic

Overall, this piece of work is 2 stars out of 5

Marked by teacher Brady Smith 01/12/2012

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