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Experiment to find how different concentrations affect the rate of a chemical reaction

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Introduction

Experiment to find how different concentrations affect the rate of a chemical reaction Aim: To find out how different concentrations of Sodium Thiosulphate (Na?S2O3) affect its reaction with HCL. The rate of a reaction depends on four things: 1. Temperature 2. Concentration 3. Catalyst 4. Surface area We can measure the speed of a reaction using the precipitate formed as a product of the reaction. By observing a marker through the solution, we can measure how long it takes before the marker is no longer visible. I am going to measure the rate of reaction with the concentration of the solution. Preliminary work: To investigate different amounts of HCL so I can find the best amount to use in my experiment I am going to test 40cm� of Sodium Thiosulphate with 10cm� and 20cm� of HCL and then with 5cm� and 10cm� of HCL. After doing the preliminary investigation I got the following results: Na2S2O3 HCL Result 40cm� 10cm� Faster 40cm� 20cm� Na2S2O3 HCL Result 40cm� 5cm� 40cm� 10cm� Faster In my preliminary investigation I found that 10cm� of HCL worked best with Na2S2O3 because there are not too much and not too little particles, therefore there's a more likely chance of a collision and 10cm� is an easy number to work with. ...read more.

Middle

4. De-concentrate the solution so it becomes 0.08molar and do the same. Record the results. 5. Continue doing this until all 5 concentrations have been tested and the results have been recorded. 6. Repeat the experiment to find the average time for more accurate results and plot the results on a graph. Prediction: I predict that the higher the concentration of Na2S2O3, the less time it will take to react because there are more particles for a collision to take place with HCL. Hypothesis: Increasing concentration increases the number of collisions. If the solution is more concentrated there are more particles of reactant between the water molecules, which makes collisions between the particles more likely. Results: Expt Concentration Time Taken Rate of Reaction 0.1m 30s 1/30 = 0.033 per second 0.08m 36s 1/36 = 0.028 per second 0.06m 53s 1/53 = 0.019 per second 0.04m 82s 1/82 = 0.012 per second 0.02m 257s 1/257 = 0.004 per second Results: Expt repeated Concentration Time Taken Rate of Reaction 0.1m 33s 1/33 = 0.030 per second 0.08m 43s 1/43 = 0.023 per second 0.06m 60s 1/60 = 0.017 per second 0.04m 85s 1/85 = 0.012 per second 0.02m ...read more.

Conclusion

Evaluation: The procedure used was accurate and enabled me to get appropriate results. They were clear and simple to follow. However if I included repeating the experiment 3 or 4 times, the results would me more accurate. In the time-concentration graph, there were many anomalous results. These were because time and concentration do not increase at the same rate. Each amount takes a different time to react, although the higher the concentration the less time it will take to react. There is a big leap between 0.04m and 0.02m concentration of HCL. This is because temperature and concentration aren't directly proportional. To improve the experiment I could use more different concentrations to see if the rate of reaction stays in direct proportion with concentration. I could also use more different concentrations to get more results, which can help prove my hypothesis. The anomalies occurred either because totally accurate amounts weren't added together or the stop-clock wasn't stopped at the right time. If I was to do this investigation 100% accurate I don't think there will be any anomalies. Further work could be to investigate temperature with rate of reaction or catalysts and see which one would be best and most efficient. ...read more.

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