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How does Concentration Affect the Rate of Reaction.

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How does Concentration Affect the Rate of Reaction Aim: I aim to find out how concentration of a chemical affects its time of reaction. This experiment will be carried out simply by mixing Hydrochloric acid and different concentrations of Sodium Thiosulphate in a conical flask and watching it react by going cloudy and so the cross, which we will place underneath the flask is no longer visible. It becomes cloudy because the sulphur particles precipitate and come out of the solution. The equation for this reaction is: Na2S2O3 + 2HCL -> 2NaCL + H2O + SO2 + S Concentration is the amount of the solute dissolved in a given quantity of a solution. In my case both Hydrochloric acid and Sodium Thiosulphate are dissolved in water, which makes them easy to change the concentration. As I will be using both but only changing the concentration of one, I will change the concentration of the Sodium Thiosulphate, as we will be using it in larger amounts0 so it will be easier. Also Sodium Thiosulphate is the more reactive of the two so the experiment will not take long to complete. Plan: In my experiment to find out how concentration affects the rate of reaction the variable I will be changing is the concentration of the sodium thiosulphate. I will be changing this concentration because, I found out when doing preliminary work that when there is a greater presence of sodium thiosulphate in the solution than hydrochloric acid the reaction takes place quicker. ...read more.


In the experiment I plan to mix a solution of sodium thiosulphate and water measuring 40ml with hydrochloric measuring 10ml, this is because we are not allowed over a total volume of 50ml, to preserve chemicals. I will mix the two in a conical flask. I will then place the flask above the paper with an 'x' on it. The observer will watch from a distance of 30cm above the flask. Once the observer can no longer see the 'x' the reaction, in my view is complete. I will repeat each molarity three times to obtain conclusive results. The measurements I will use for the different concentrations are: Molarity (mol dm-3) Sodium Thiosulphate (ml) Water (ml) 0.02 8 32 0.04 16 24 0.06 24 16 0.08 32 8 0.1 40 0 I am going to time the experiment for the time the two solutions are mixed together in the conical flask until the cross on the paper is no longer visible. The degree of accuracy I will use is split seconds fro the most accurate results. Prediction: I predict that the rate of reaction will increase as the concentration increases. I think this because have predicted this due to the knowledge I have gained through my research. I found out that if I want to predict he rates of reaction, the collision theory would be useful to know about. ...read more.


We used the most accurate method of timing as possible, to a hundredth of a second, so if there was a error with that there was not much that could improve it. The results were mainly good, there are no anomalous results, which did not match with the general trend of the results on the graph and everything came out as expected. Although all the average times and rates of reaction all conform to a pattern, they are not all evenly spaced and therefore are probably not perfect. The experiments were carried out fairly but it could have been even fairer. One factor that could have contributed to the slight imperfections in the results could be the varying temperatures. As temperature can also affect the rate of reaction this may have altered our results slightly, if we did this experiment again this could be avoided by doing the experiment in a temperature-controlled environment. Another factor could be as the reaction was finished when the red cross on the paper disappeared and this is only seen by the naked eye. With the whole class doing this with different eye types, there is no exact fairness in the experiment. Using devices such as a light sensor can solve this problem. The light sensor will pass through the flask were a reaction is taking place to a receiver. When the light sensor cannot reach the receiver, the timing will be stopped automatically. This will bring fairness to experiments to test all similar to rate of reaction. James Taylor 11MA ...read more.

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