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Investigating Rates of Reaction

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Investigating Rates of Reaction AIM: To investigate the effect of concentration on rates of reaction using Sodium Thiosulphate and Hydrochloric Acid. Sodium Thiosulphate + Hydrochloric Acid > Sodium Chloride solution + Sulphur Dioxide + Sulphur Na O > Na Cl + SO + S Hypothesis: The possible variables I could investigate could be: * Volume of liquid * Concentration of Sodium Thiosulphate * Concentration of Hydrochloric acid * Stir Quantity I have chosen to vary the concentration of the Sodium Thiosulphate to see how his effects the rate of the reaction. I think that lowering the concentration of the Sodium Thiosulphate in the same volume of water will cause the reaction to slow dramatically. This is because of the collision theory. The collision theory states that before a chemical reaction can take place the atoms, molecules or ions of a substance must collide. The more reactions that take place the faster the reaction. This is because when atoms, molecules or ions in a substance collide they speed up the reaction. ...read more.


First I tested 5ml of HCl. I found when testing the more diluted concentrations of Sodium Thiosulphate that the reactions were taking extensive amounts of time to finish. This would have jeopardised my ability to obtain more results in the time allocated. At 10ml the time taken was significantly more reasonable and was still safe. This led me to decide upon this volume of acid to use in the actual experiment. DIAGRAM: METHOD: 1. We will set up the apparatus as in the diagram above. 2. We will draw a black cross on a sheet of A4 paper and place it under the chromical flask so it is only visible when the solution is clear. 3. We will fill the chromical flask with the necessary concentration of the Sodium Thiosulphate with the 10ml of HCl (which we found was safe in the preliminary work) to form the controlled volume. 4. We start timing when the whole volume is in the chromical flask. 5. Stop timing and record the result when the black cross is completely invisible. ...read more.


Even through trying to do this from the same point every time it was still a very inaccurate process. Also there was a problem with the Sodium Thiosulphate decomposing due to the experiment having to be separated into two days. We had a slight difficulty controlling the temperature in the investigation. In the first day the sun was shining and the heat was present whereas on the second the weather was dull and therefore less heat. My results were approximately anomaly free and were about 85% accurate. If I were to do the experiment again I would try to conduct all the results in one day as to limit the rotting of the Sodium Thiosulphate. I could extend my investigation further by I could investigate the effects of increasing the volume, the effect of temperature or the effects of stirring. Another factor I could choose to measure is the rate of reaction. In this experiment the rate of reaction (Time taken for reaction to take place/change in amount of substance) is the inversely proportional to 1/ time taken. These results would have been more conclusive when these were present as the rate itself could have been examined instead of results. ...read more.

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