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See how long it takes for sodium Thiosulphate and hydrochloric acid to react at different concentrations.

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Disappearing cross investigation Aim: To see how long it takes for sodium Thiosulphate and hydrochloric acid to react at different concentrations. My Hypothesis: Using the idea of the particle theory, the more dilute a solution is, the more time it will take for the particles to react. This is due to the fact that the particles have less energy reducing the collisions and the speed of which they collide, therefore taking longer to react. I predict that the more water I add to the solution the longer it will take the cross to not be visible. Variables: In this experiment I will only need to decrease the concentration of the Thiosulphate and I will need to increase the concentration of the water. All of the other factors I shall keep the same. To keep the experiment in a fair I will make sure that all the measurements that I take are as accurate as possible. I will also make sure that all the timing is exact. I will stir the each solution for the same amount of time each time so that it is fair. ...read more.


I shall then collect all my equipment and place it at the table so that I am ready to start the experiment. I will then draw up a table of results ready to take down each result as soon as they come. Now ready to start my first experiment I shall measure 50cm� of sodium thiosulphate. I will then also measure 10cm� of dilute hydrochloric acid. Once I have both of the measurements I shall first pour the sodium thiosulphate into a conical flask that has been placed above the cross. Once I have done that I will then pour in the dilute hydrochloric acid. As soon as I have poured it in I will then start the stopwatch. After 5 seconds I will stir the solution for 15 seconds exactly, no longer and no less for all the experiments to keep the test fair. Once the cross has fully disappeared I shall stop the time and take the reading down. I will repeat this 3 times so that the experiment is fair and accurate. For the first experiment I used only sodium thiosulphate and added no water. ...read more.


Overall my experiment worked well. There was one anomalous result in the experiment. That was for the 40cm� of water and 10cm� of sodium thiosulphate. As you can see on the graph above there was a steady increase in the times then for the last one there was a large gap. This could have been because there was too little sodium thiosulphate and it was very dilute therefore it had less energy and took a long time to react. I feel my evidence was as accurate as it could have been apart from the last time which I feel was an anomalous result. Anomalous Result Improvements I feel that the experiment was fairly accurate but there was still a need for improvement. To make it more accurate instead of using a cross you can use a light meter. You place the light meter in the place of the cross and shine a light from the top of the beaker. When the light meter cannot detect anymore light due to the precipitation (cloudiness) formed it will take an automatic reading. This will make the experiment much more accurate and less prone to human error. I could have also improved my investigation by redoing the experiment which got me the anomalous result so that I could have got a perfect result and as accurate as possible. ...read more.

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