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Investigate the effect of concentration on the reaction between Thiosulphate ions (S2O32-) and H+ ions.

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(1) Skill area P: PLANNING Problem: Investigate the effect of concentration on the reaction between Thiosulphate ions (S2O32-) and H+ ions. Introduction: When sodium Thiosulphate solution reacts with acid, a precipitate of sulphur forms. The time taken for a certain amount of sulphur to form can be used to indicate the rate of reaction. In this experiment the effect of concentration of sodium thiosulphate on the rate of this reaction is investigated. Prediction: I predict that as the concentration of sodium thiosulphate, (Na2S2O3) in MoLdm-3 increases it will take a shorter time for the sulphur precipitate to form. Thus: * The higher the concentration, the faster the rate of reaction. This is also vice-versa, * The lower the concentration the slower the rate of reaction. Background Information: Collision theory: If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. Also, When the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully. If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself: For a reaction to occur particles have to collide with each other. ...read more.


I expect my 2 graphs to look like this. The average time graph should have a smooth curve and the Rate 1/Time graph should be a straight line. Calculations: To work out the rate of reaction you simply divide 1 by the time taken. For example if the time taken is 30 seconds - 1 / 30 = 0.033333333. This value would be difficult to plot on a graph so I then multiply this value by 1*10 3. In other words by 10000. So we represent the rate as in the case of 0.33333333 as 33.3*10 -3. So, Rate of reaction = 33.3*10 -3 To calculate the average time you simply take the first time and then add the second time. With this value you divide by 2. So if the first time is 30 seconds and the second time is 35 | 30 + 35 = 65 / 2 = 32.5 | Average time = 32.5. Will my results be precise and reliable? When I take 2 different readings for each different concentration this increases reliability of the results and by taking the average time of my results this is increasing the reliability of them. So the results for the time taken should be valid. But the other factors e.g. light intensity, temperature, the swirling of the flask all must remain constant. If this is all takes place my results should be precise. If I use more accurate equipment to measure out the different volumes of chemicals I could make my results more accurate. ...read more.


I believe that I could have improved the method by making it more specific. I stated clearly all the various methods I took in setting the experiment up but I could have been more specific to how all the apparatus was used and perhaps why I used the apparatus I did as well. Some other areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of sodium thiosulphate and hydrochloric acid. There is lots of room for human error here. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment. Overall, this investigation has been a very successful one. I feel my results and analysis have been as accurate and reliable as they could have been under the time allocated. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables i.e. temperature or adding a catalyst. To really improve my results I could have changed to recording the time by not just looking down from above at the cross disappearing, but by using computer and data sensors to record the times. This may be more accurate than my own assessment of the cross disappearing. I could also obtain a larger number of readings and possibly use a wider range of concentrations. I could use this method using light sensors to see when the precipitation is formed, and also for temperature, by using temperature sensors. Liam Brogan. S2F. This document was downloaded from Coursework.Info - The UK's Coursework Database Click here to visit Coursework.Info/ ...read more.

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