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The effect on the rate of reaction by changing the concentration of a reagent.

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The effect on the rate of reaction by changing the concentration of a reagent Introduction: The main objective in this investigation is to find out what effect an independent variable has on a reaction between hydrochloric acid and sodium thiosulphate. When sodium thiosulphate and hydrochloric acid react they produce a cloudy precipitate. Both of the solutions are clear yet react together and produce a yellow precipitate of sulphur. The equation for the reaction is as follows: Na2S2O3 + 2HCl 2NaCl + SO2 + S + H2O As the two substances react in the neutral medium of water the rate of reaction is easily observed by a disappearing cross placed underneath the beaker in which the sodium thiosulphate, hydrochloric acid and water react. Plan: First the apparatus (above) is to be set up, followed by the conduction of the experiment. There are a few variables that will not be changed purposely. These are called the controlled variables. Such as the temperature, light and human error. Surface area will not affect the reaction as both chemicals being used are already aqueous. ...read more.


The rate of reaction therefore decreases. This is because the water is not reactive, the only two reagents in the solution are sodium thiosulphate and hydrochloric acid, if there is more water and consequently less of one of the reagents, then the other will find it harder to find another substance to react with. The prediction was that as the concentration of the two reagents increased and the concentration of water decreased then the rate of reaction would also increase and the time taken for the cross to disappear would decrease. The results showed that the prediction was right because the theory of activation energy was developed and always works at one-hundred percent accuracy. Although the prediction was correct in general one of the results was anomalous and uncharacteristic of the other results. This anomalous result affects the concluding segment of the investigation because this now shows that the experiment is not one-hundred percent accurate. However, in conclusion it is almost certain that as the concentration of sodium thiosulphate is increased and the concentration of water is decreased to a designated amount of hydrochloric acid then the rate of reaction will also increase and the reaction time will decrease. ...read more.


It is believed that the anomalous outcome that took place was result of not adding the correct measurements of each reagent, or possibly not adding one of them! It is not thought however, that the "activation energy theory" is wrong or does not always work. The anomalous result was ignored and not counted towards the final average or rate of reaction. To avoid such results in any future repetition of the same investigation the chemicals will be stored in two completely different areas. A new conical flask is to be used for each experiment to save time washing up and attempting to keep the paper with the cross dry and more results will be taken to ensure that the average taken at the end is much more accurate. For example, at the moment, if one of the results taken is anomalous then one third of the results from those concentrations of reagents are not able to be used, but if instead of three attempts for each concentration test ten are used then only one tenth will have to be rendered useless. By James Bailey 10.7 ...read more.

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