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Kinetics of the Acid-Catalyzed Iodination of Propanone

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Introduction

Name: Kayla Jackson Date: 10th of May Partner's name: Shu Ean Wong Kinetics of the Acid-Catalyzed Iodination of Propanone Introduction Research - The aim of this investigation is to calculate the values of x, y and z and hence the overall order of the reaction. Prior to proposing a possible mechanism for the reaction that is consistent with the suggested rate equation. The value of k, the rate constant will also be determined for this reaction at the temperature (room temperature) at which the experiment was conducted. The reaction between iodine and propanone involves only one coloured reagent, being that of iodine. "This immediately suggest that the reaction would be quantifiable" via colour based analysis such as that of a spectrophotometer, or merely by timing a visual analysis of the reaction and then henceforth calculate the rate from the time of the iodine to be completely reacted. Any changes in the rate of the reaction will therefore be solely due to the changes in the Iodine concentration. The order of the rate of the reaction is determine through a theory referred to as initial rates. These initial rates are used in order to measure the rate of reaction before the reactants have been completely used up. This is done by drawing a tangent from when time is equal to zero on a time verse concentration graph, prior to working out the rate from the gradient of the tangent (assuming no change has occurred to the concentrations of the reactant). Once the initial rate has been determined a graph of rate against concentration of a reactant can be created. This will then be used in order to determine the order of the reaction in respect to iodine. The graphs shown below depict what these graphs would look like for the different orders of reaction. Data Collection and Processing Qualitative Observations - As each trial for this experiment was conducted by another group, it is difficult to classify the qualitative observations ecologically valid. ...read more.

Middle

Rate of Reaction for solution A= 0.4 m mol dm-3 / 50.13 seconds = 0.008 m mol dm-3 sec-1 Rate of Reaction for solution B= 0.8 m mol dm-3 / 25.56 seconds = 0.031 m mol dm-3 sec-1 Rate of Reaction for solution C= 1.2 m mol dm-3 / 15.98 seconds = 0.075 m mol dm-3 sec-1 Rate of Reaction for solution D= 0.4 m mol dm-3 / 30.05 seconds = 0.013 m mol dm-3 sec-1 Rate of Reaction for solution E= 0.4 m mol dm-3 / 11.91 seconds = 0.034 m mol dm-3 sec-1 Rate of Reaction for solution F= 0.4 m mol dm-3 / 23.60 seconds = 0.017 m mol dm-3 sec-1 Rate of Reaction for solution G= 0.4 m mol dm-3 /15.86 seconds = 0.025 m mol dm-3 sec-1 Though the reaction rate for each of the solutions was calculated only those with differing concentrations but the same variables (the concentration of the other substances tested) were utilized in the graph for the sake of control said variables. As such for Propanone the solutions graphed are that of A, B and C. Graph 2 - The average calculation of rate against concentration for the different concentrations of Propanone. When examining the graph it is possible to determine that there is an apparent increase in rate with an increase in concentration. When compared with the diagrams of the different order of reaction it can be suggested that this indicates that the concentration of iodine does affect the concentration of the reaction and as this appears to be that of a linear relationship it can be suggested that is is a first order reaction in regards to Propanone. Though the y-intercept is not at that of zero however indicates that it may be so and due to the fact the gradient is positive indicates that there is a proportional relationship between concentration and rate. ...read more.

Conclusion

The temperature is considered to have remained relatively constant throughout the experiment and as such is likely to have affected the percentage error rather than individual results. Despite this, if it had this would have greatly reduced the reliability of the data between the differing conditions and hence have affected the rate constant. Method of Improvement: It would be possible to monitor the temperature through means of an air conditioner and thermometer. Another way in which to do so would be to place the reactants in a water bath and then set it to the same temperature as that mentioned within the literature researched. Human Reaction Rate to Colour Change Effect on Results: Relying on different individuals from different groups in order to determine the time for the reaction to occur is incredibly inaccurate. It reduced the reliability as the different groups may perceive colour change different, they may have eye troubles or the test tube may be tinted, as was believed to have occurred. Method of Improvement: Repeated trials, by the same experimenter will help to lower the number of inconsistencies. Another way to ensure more accurate acknowledgement of the colour change and therefore completion of the reaction would be to utilize a UV-Vis spectrometer in order to accurately calculate when the reaction has a similar value to that of a control set. Human Reaction Rate to Timing Effect on Results: This variance to when each group decided to classify the reaction as complete and therefore stop timing significantly reduced the precision of the results and each person had their own specific value. Sometimes the groups would debate as to when the colour change actually occurred and as such each experimenter's individual standards for reaction change will affect the time noted. Method of Improvement: Similar to that of the improvement to the perception of colour change, having only one person, with their own interpretation that remains constant will allow for greater precision with the timing, however with this being said it also may reduce the accuracy, as the individuals own perception may be hindered or biased. ...read more.

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