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# detremining the rate equation

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Introduction

The determination of a rate equation Aim The aim of this experiment is to plan an experimental procedure leading to a graphical method to determine how the concentration or the volume of the components affects the rate of the reaction whose equation is given below: 2HCl(aq) + Na2S2O3(aq) --> 2NaCl(aq) + SO2(g) + S(s) + H2O(l) Introduction In this experiment in order for the reaction to take place the reactant particles must collide, and only some of those colliding particles lead to a chemical change. The rate of reaction is defined as the amount of in moles of a reactant which is used up in a given time, in this case it's the amount of sulphur formed in a given time. To work out the rate equation I will conduct two methods. In order to relate the rate of reaction with the concentration of the components involved I will have to obtain results to help me determine the rate of expression of the reaction. There are two methods used to determine the rate expression. This is done by measuring the concentration over time. The concentration has to be measured throughout the reaction. From the results obtained graphs are drawn and from that the order of the reaction is determined. The reason I'm not using this method is I don't have the right equipment to do that. The concentrations will be constantly changing and therefore making it harder to keep track of and record. Therefore I'm going to use the other method. The method I will use to determine the order of the reaction is initial-rate method. This method is used when the initial concentrations of the reactants that are going to be mixed together in the reaction flask, from this the initial rate of the reaction can be found. From my experiment I will obtain the time taken for the reaction to take place, from that I will work out the rate of the reaction and plot graphs of rate against concentration. ...read more.

Middle

Conclusion

It was hard to decide when to start the stopwatch and when to stop it. I t was very hard to judge whether the cross disappeared or not. As the solution started to get cloudy and the cross was about to disappeared there was at least a 5 second gap where the solution will be at the same intensity and this lead to the most significant error. Where you would be unsure whether the reaction has come to completion or not. In order to draw the graph the rate had to be worked out, dividing one by the time taken and if the timing error was around 5second this will be a major different in the value obtained and this will lead in anomalous results. So in the future to avoid this significant error I would use a colorimeter. I can also use a light sensor which more suitable for this type of experiment. This will measure the amount of light passing through the solution. The light sensor will have a fix point when to stop the timing. It will stop timing when the there is no light passing through the solution. And this will result in a more accurate and reliable results. If a calorimeter was used it would measure the amount of light adsorbed by the solution. An appropriate filter would be used allow only certain colour though. As the solution gets cloudy and starts to change colour the amount of light absorbed by the solution will also increase. When all the light is absorbed by the solution the timing should stop. To make this more accurate I will link the colorimeter to a data logger which is in turn linked to a computer where accurate timing will be recorded. I can also stir the solution to help me obtain more reliable results. This will enable all the particles to interact with each other. To get the most out of this method will have use a machine that will stir all the solutions at the same speed. ...read more.

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