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Changing the speed of a Chemical Reaction

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Changing the speed of a Chemical Reaction Introduction: Hydrochloric acid reacts with Sodium Thiosulphate to make sodium chloride, sulphur dioxide and sulphur. Sulphur appears as a yellow deposit. The Equation for the reaction is: - Sodium Thiosulphate + Hydrochloric acid --> Sodium Chloride + Sulphur dioxide + Sulphur Na2S2O3 + 2HCL --> 2NaCl + SO2 + S Task: To investigate what effect changing the concentration of the Thiosulphate has on the speed with which the sulphur materializes. Prediction: As the concentration of sodium Thiosulphate is increased, I predict that the rate of reaction will also increase. I think this because as the sodium Thiosulphate concentration is increased it will react more quickly with the hydrochloric acid as it is more concentrated there are more sodium Thiosulphate particles so therefore a much more chance of a sodium Thiosulphate particle colliding with a hydrochloric acid particle with enough energy for a reaction to occur and this results in less time taken for the solution to become cloudy as the sulphur is precipitated and the cross to become invisible. ...read more.


* Repeat for other dilutions of Sodium Thiosulphate Results Table: Sodium Thiosulphate (cm3) Distilled Water (cm3) Hydrochloric Acid (cm3) Time taken in seconds for x to disappear Average (Seconds) Exper iment 1 Exper iment 2 50 0 10 20 19 19.5 45 5 10 23 22 22.5 40 10 10 27 21 26 35 15 10 30 26 27.5 30 20 10 39 35 36 25 25 10 45 40 44 20 30 10 50 49 49.5 15 35 10 65 63 64 10 40 10 110 113 111.5 5 45 10 250 279 264.5 I originally planned to do each experiment 3 times, but due to the shortage of time I was limited to only repeating each experiment twice. In the column labelled Experiment 2 I have highlighted my 3rd reading in Red because it seemed unusual to me. I repeated the experiment a third time and got 25 seconds. I was content with this result because it was closer to my first reading. ...read more.


Using the graphs, I can draw a conclusion from my experiment. Firstly I can see that with the "time" graph (that plot concentration against time taken for the reaction to take place) the graphs have negative correlation in both cases, meaning that as the concentration increased the time taken for the reaction to take place decreases. For this to fully make sense it is necessary to recap the collision theory briefly: For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area. MOHAMED PANCHBHAYA 11L SCIENCE COURSEWORK CANDIDATE NUMBER: 2838 ...read more.

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