Kinetics of the Acid-Catalyzed Iodination of Propanone

Name: Kayla Jackson

Date: 10th of May

Partner’s name: Shu Ean Wong

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. Despite this it was possible to make some observations as to why the particular trial conducted by the experimenters’ one particular trial, varied from the other results while making speculations as to why some of the other trials had certain results. It was observed that the groups were having difficulty determine whence the colour change had taken place. The time of colour change were often disputed between the student group members indicating the effect of human error.

Other observations included that of the gradual colour change of the iodine prior to being added with the Propanone. It was also noted that one of the burettes was leaking, indicating that some of the measurements of each solution. It was also noted that some of the test tubes were made of a thicker glass, with a green hue. For one experimental group in particular, that for Solution D for group 3, the members were unaware of such fact until after a great deal of time had passed as a disagreement between the group as to when to stop timing despite the hue had prevented them from calculating at the time in with the yellow colour of iodine was no longer present.

Raw Data Table –

Table 1: The Time Taken for Iodine of different concentrations to decolorize.

In was assumed that he percentage uncertainty of the stock solutions provided would be that of 1%. As the burette had an absolute uncertainty of 0.005 mL, it was assumed that in taking two separate measurements each time when adding the certain number of moles of each of the four solutions., Therefore it is necessary to multiply 0.01 mL by the four different solutions and then determine the overall percentage uncertainty of the solutions. 0.04 mL uncertainty of a 10 mL solution is 0.4%, which when adding the uncertainty of the original solution is equal to that of 1.4%. As the concentration of iodine is measured to a lowest figure of 0.25, two significant figures, it was decided that all values of concentration will thence need to have two significant figures.

Table 2: Original concentration and ratio of each solution used for the mixtures.

Each experiment corresponds to a concentration of the iodine which can be calculated by the following formula:

Table 4:

Overall Concentration of Iodine = Concentration x (volume of iodine / total volume)

Table 5:

Overall Concentration of Propanone = Concentration x (volume of Propanone / total volume)

Table 6:

Overall Concentration of Sulfuric Acid = Concentration x (volume of sulfuric acid / total volume)

Table 7: Concentration and ratio of each solution used for the mixtures.

Data Processing

Overview – The experiment was replicated by 5 different groups in order to allow for random errors. Therefore in order to attempt to graph the results, it was decided to average time for the iodine within the reaction to become clear. The concentration of the iodine solution each had an associated percentage uncertainty and the time also had such associated uncertainty, however in by averaging the results it was deemed that the use of standard deviation from results would be a better indicator as to the consistency of the average results.

The aim ...