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An investigation into how concentration affects the rate of a reaction

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Introduction

An investigation into how concentration affects the rate of a reaction PLANNING AIM The aim of this investigation is to see how differing concentrations of a solution affect the rate of a reaction. In this case, the solution is Hydrogen Peroxide solution (H2O2) and the catalyst is Manganese Oxide (MnO4). VARIABLES The variables that must be controlled in this reaction are: * Temperature * Concentration of solution * pH * Time * Catalysis * Surface area of catalyst (powder or granules) * Volume/Mass (solution/catalyst) The variable I have chosen to control is the concentration of the solution. HYPOTHESIS The reaction that I plan to measure is: MnO4 2H2O2 = 2H2O + O2 I believe that as the concentration of the solution increases, the rate of the reaction will also increase, in the same ratio. Further to this, this will be in a directly proportional ratio, giving a straight-line graph through the origin on a 'rate against concentration' graph. However, this rate cannot continue exponentially, there must be a 'peak rate of reaction', where the rate cannot increase further. This will mean that the graph flattens off, giving a plateau effect. This is what I estimate the graph to look like: Rate (grams of O2 released/minute) Concentration This hypothesis can be explained by a simple quotation from, Chemistry, An Experimental Science: "By increasing the concentration of a solution, the number of particles in a given volume increases, giving more frequent collisions. ...read more.

Middle

If all these are adhered to, then I can be sure that the experiment will be a fair one, and that all results gained will be just. SAFETY The hydrogen peroxide that I plan to use is only a mild irritant, but I will still wear goggles, an apron and take care then using this acid. As the reaction is quite a violent one, I will also have to take care that I have set up the apparatus correctly, as at the higher concentrations the gas can be released at a fast rate. These precautions should ensure that the experiment is carried out safely. ANALYSIS Taking the results collected in the experiments, I drew two graphs. The first graph plots all the figures collected for of 'rate of gas collection' for each concentration, against the concentration. This is done to give an idea of the spread of the data collected, and to identify any anomalous points. The second graph plots the average figures for the 'rate of gas collection' against the 'concentration of the H2O2' used. The averages were calculated by removing the anomalous pints identified in graph 1, then finding the mean. It is the second graph that I shall use to formulate my conclusions. Using Graph 2, I can conclude that the concentration of a solution is directly proportional to the rate of reaction in which that solution is involved. ...read more.

Conclusion

If I started with a stronger H2O2 solution, such as "40 volume", then I could investigate the plateau effect. * I could use a mass balance with an accuracy of up to 0.001 grams. This would greatly increase the accuracy of results. * More repeats are always desirable, I suggest doing 3 more sets. * I plan to use the powdered version of the MnO4, as this removes the problem encountered by the varying size of granules. * I could increase the volume of H2O2 used to 20cm3, and the mass of powdered MnO4 to 1 gram. This would give a larger spread of results, as more gas would be collected, and so give a truer representation of the data. * Due to the problems encountered with the depletion of the H2O2 over time, I shall use the same source of the solution, meaning it will all have reacted to the same level. If the H2O2 used is old, part of it will have reacted to become water (2H2O2 = 2H2O + O2), and so will have a lower concentration. Using the same source will remove this issue, resulting in a higher level of accuracy in my results. In summary, my experiment provided successful results. The methods used were not always as reliable as would be desired, and my prediction was not tested fully due to the small range of concentrations used. Despite this, I can still say that concentration of a solution is directly proportional to the rate of reaction. CHRISTOPHER KURWIE Chemistry Sc1 - Planning 11PS Page 1 of 8 ...read more.

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