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Chemistry Concentration effects rate of reaction

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Introduction

How does concentration affect the rate of a reation In this experiment I will have to look at how concentration affects the rate of reaction. I will have to decide which concentrations to change, and the reaction that I will be performing. Prediction The reaction I have chosen is: Sodium + Hydrochloric ==> Sulphur + Sodium + Sulphur + Water Thiosulphate + Acid Chloride Dioxide Na2S2O3 (aq) + HCL (aq) ==> S(s) + 2NaCl (aq) + SO2 (g) + H2O (l) There are many different things I can change which will affect the rate of reaction, so I will have to do preliminary experiments to find out ideal quantities for my final experiment. Below are some variables I can change for my experiments: o Temperature o Concentration of Sodium Thiosulphate o Concentration of Hydrochloric Acid o Volume of Sodium Thiosulphate o Volume of Hydrochloric Acid o If I stir the experiment or let it stand For this reaction I will have to decide a suitable quantity of Sodium Thiosulphate and Hydrochloric acid during my preliminary investigations, then I will have to decide whether I will be changing the concentration of the Hydrochloric Acid or the Sodium Thiosulphate. The reaction takes place relatively quickly and relies on the naked eye. I will be having to time how long it takes for an image below the conical flask in which the reaction taking place, gets entirely obscured by the build up of sulphur. ...read more.

Middle

Preliminary Investigation 2 For the second preliminary investigation I chose to test the concentration of the hydrochloric acid. I tested using 20cm of hydrochloric acid at different concentrations, 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% and 10%. The results are below. HCL (cm) Water (cm) Na2S2O3 (cm) Time Taken (Seconds) 20 0 50 37 18 2 50 38 16 4 50 40 14 6 50 42 12 8 50 45 10 10 50 46 8 12 50 47 6 14 50 48 4 16 50 56 2 18 50 86 I chose to use hydrochloric acid at 100% for the main experiment. Main Experiment For the main experiment I chose to change the concentration of the Sodium Thiosulphate. I will be testing the concentrations 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% and 10% and recording the results. I will then plot two graphs, a time graph, and a rate of reaction graph. Results: HCL (cm) Na2S2O3 (cm) Water (cm) First Experiment (s) Final Experiment (s) Increase in Time (s) 5 50 5 40 43 0 5 45 10 49 48 5 5 40 15 54 52 4 5 35 20 58 57 5 5 30 25 66 66 9 5 25 30 75 72 6 5 20 35 120 112 40 5 15 40 234 212 100 5 10 45 382 370 158 5 5 50 447 451 81 On the next page I have drawn a graph to show the time taken for the reaction. ...read more.

Conclusion

I also feel that the reaction was unfair due to inaccurate measurement, all measurements relied on the naked eye and may have not been the measurement we wanted, but appeared to be. I think that a way to make them fairer would be to use scales and weigh the chemicals, or use a pipette. Both of these methods are more accurate, but are much slower. In the main experiment I found some odd results, but retested them and they 'fitted in'. The original results may have not been as accurate as there may have been contamination, inaccurate measurements or different lighting making the image seem to disappear quicker. I also feel that the reaction is an unfair one to test as it relies on the naked eye to tell when the image has been obscured completely. This can be difficult as different lighting levels can make it easier to see and sometimes the human brain may fool you into thinking the image is still there. I could change my method to make it more fair I could use lasers instead of the eye to see when the image has 'gone'. I would place lasers on each side of the beaker, when the laser beam path gets fully obscured by the build up of sulphur, the beams would get 'cut' and the computer will accurately record when this has happened. ?? ?? ?? ?? Page 5/10 ...read more.

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