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To investigate a factor that affects the rate of reaction and why?

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Introduction

Coursework Assessed Practical An Experiment to investigate the rate of reaction Name: Ruth Fitzpatrick Aim: To investigate a factor that affects the rate of reaction and why? Introduction: I am going to investigate what factors affect the rate of reaction. In particular I will look at how the concentration of the reactants affects the speed of the reaction. To do this I am going to add sodium thiosulphate to different molarities of hydrochloric acid and time how long it takes for the reaction to take place. The equation is as follows: Sodium Thiosulphate + Hydrochloric Acid � Sodium Chloride+ Sulphur Dioxide+ Sulphur + Water (Yellow insoluble solid - precipitate) Na2 S2 O3 + 2H+ CL- � 2Na+CL- + SO2 + S + H2O The chemists who work in industry have to try and produce materials as cheaply as possible. Efficiency is important, and to create an efficient reaction in industry, it should be quick. In order to do this they want conditions, which increase reaction rates. These conditions are also the factors involved in this investigation: To increase a reaction rate the number of collisions between particles must be increased, this can be done by: > Using a suitable catalyst (substances, which speed up chemical reactions without being affected themselves). > Increasing the temperature of the reactants will enable the particles to move around quicker. Therefore there will be more collisions. > Increasing the surface area - when the surface area is smaller (if you had a big lump of matter) the reaction takes longer, because there is only a small surface area for the particles to react. However if the lump were broken into a powder the reaction would occur much faster as the availability of particles for the reaction would increase. > Increasing the concentration of reactants - a concentrated solution contains a lot of particles dissolved in a solvent, which means more chance of particles colliding and reacting. ...read more.

Middle

So the average rate of reaction will be: m/t Since m is constant we can write: I have now redrawn my results table without the anomalous results, recalculated the average and added the rate of the reaction: Table showing results, average time the reaction took and rate of reaction excluding anomalous results Concentration of HCl (molars) Time taken to obscure cross from view (secs) Average time of reaction (secs) Average Rate of Reaction (1/t) (to 2dp) Test 1 (secs) Test 2 (secs) Test 3 (secs) 0.2M 172 167 - 169.5 0.0059 0.5M 108 113 - 110.5 0.0090 1M 92 94 99 95 0.0105 1.5M 98 91 - 94.5 0.0106 2M 77 90 83 83.33 0.0120 NB - Average time of reaction in seconds is correct to 2 decimal places. Average rate of reaction is correct to 4 decimal places. Results from Graph 1: On graph 1 I have circled in green the results that I believe to be anomalous, as they do not fit the pattern. I have then drawn a curve of best fit excluding these results. The curve reinforces what I said in my analysis of the results table; there is a strong pattern in my results, as the concentration increases the time of the reaction decreases. However, my graph also shows the amount of decrease in the time the reaction takes between each concentration, decreases as the concentration increases. The curve shows it is an inverse graph; therefore it is a negative correlation. I will now draw a second graph to show the rate of reaction against concentration. This should show me a positive correlation; therefore the curve should go the opposite way to the curve on graph 1. This is because the rate of reaction increases as the concentration increases. Results from Graph 2: I have now drawn my second graph. From my results and the two graphs I have drawn so far I can see that my prediction was correct, the higher the concentration of the reactant, the higher the rate of the reaction, and the shorter time it took for the cross to be obscured from view. ...read more.

Conclusion

There are several possible reasons for these anomalous results. However, I feel it is most likely to be down to the faulty concentration of acid and the difficulty judging when the reaction had reached the end point. If I were to repeat the experiment I would make some alterations. Firstly I would improve as many of the above things as possible within the confines of school. I would repeat the experiment more times for each concentration and would also extend it in other ways. These could involve doing more concentrations within my range or dong a wider range of concentrations. I could also look at the other variables of this reaction, such as catalysts, or look at other reactions and the concentration of one of the reactants affects them. I could also use the computerised light sensor instead of doing it by eye. To further this investigation I could perform a different experiment. I would be interested in doing an experiment to investigate whether temperature or molarity has a bigger influence on time of reaction. To do this I would repeat the experiment above making the changes I have already outlined including the use of the light sensor. However for each concentration I would change the temperature. Sot eh first three times I would put ice around the beaker containing the reactants. I would make sure both the reactants were the right temperature separately (using ice for example) with a thermometer. I would then make sure they were sustained at that temperature for the experiment. I would repeat this three times for each concentration. I would then do it at room temperature and then do the experiments while the reactants are hot. However I will have to be careful not to evaporate any of the solution. From this information I should be able to compare the extent temperature has on rate of reaction with the extent molarity has on the rate of reaction. Ruth Fitzpatrick 11S 1 ...read more.

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