Iodine Propanone Coursework

Unformatted text preview: Experiment to study the kinetics characteristics of iodination of propanone using a colorimeter Abstract Iodine gives a deep yellowish brown colour in aqueous solution. As propanone is iodinated and iodine is converted to iodide ion, this colour slowly fades as iodine is consumed. Thus iodination of propanone can be investigated by the change in absorbance. In the investigation, kinetics of this reaction has been studied colorimetrically. The extent of the reaction has been monitored by measuring the absorbance in the visible region of wavelength 545 nm. There is a decrease in absorbance indicating the consumption of iodine. H + ion acts as a catalyst in this reaction. Thus, the kinetics of iodination of propanone has been studied in the presence of hydrochloric acid. Introduction As the following reaction proceeds, The concentration of iodine decreases and the brown/yellow colour intensity of the reacting solution also decrease. For dilute solutions, absorbance is proportional to concentration. Decrease in concentration of species can be measured by the change in absorbance. Mechanism for the iodination of propanone: Experimental procedure Calibration of the spectrophotometer The spectrophotometer is switched on to allow it to warm up. The wavelength of the apparatus is set at 545 nm. Since iodine solution is reddish, it can absorb cyan light which is the complementary colour to red. The apparatus is then calibrated using distilled water (blank). Preparation of reaction mixture 10 cm3 of iodine solution, 10 cm3 propanone, 10 cm3 of 2.0 mol/dm3 HCl and 10 cm3 water is measured using a 10 cm3 pipette into different test tube. Quickly the following solutions in a conical flask and start the stop watch. The reaction mixture is poured in a cuvette and inserted in the spectrophotometer the absorbance of the reaction mixture is noted after each 30 second of time interval until the reaction is over. The data is recorded and a graph of absorbance against time is plotted. Calibration curve Two solutions A and B are prepared as follows: Solution A/cm3 10 10 20 Reagent Propanone Iodine solution Water Solution B/cm3 10 0 30 To prepare the calibration curve, a series of different concentration of iodine solution are made as suggested in the Results table 1. Results table 1 Experimen t number 1 2 3 4 5 6 7 8 9 10 11 Solution A/cm3 Solution B/cm3 0.0 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Concentration of I2 (10-3 mol/dm-3) 0.00 12.5 11.25 10.0 8.75 7.50 6.23 5.00 3.75 2.50 1.25 A series of different concentration of iodine are placed in the cuvette and the corresponding absorbance are measured and noted. A graph of absorbance against concentration of iodine is plotted to obtain a calibration curve. The calibration curve is used to convert the spectrophotometer reading to iodine concentration. A graph of concentration of iodine against time is plotted to determine the rate and the order of the reaction between iodine and propanone. Recorded data Absorbance of the reaction mixture Time/min 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 Time/min 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 Absorbance 1.212 1.008 0.85 0.705 0.56 0.41 0.269 0.163 0.11 0.098 0.096 0.095 0.096 0.096 0.097 0.097 0.097 0.098 0.098 0.099 0.100 0.100 0.101 0.101 0.102 0.103 0.103 0.104 0.104 0.104 0.104 Graph of absorbance against time for a period of 15 minute 1.4 1.2 1 0.8 Absorbance 0.6 0.4 0.2 0 0 2 4 6 8 10 12 Time/min Graph of absorbance against time for a period of 5 minute 14 16 1.4 1.2 1 0.8 Absorbance 0.6 0.4 0.2 0 0 1 2 3 Time/min Calibration curve Concentration of I2 (10-3 mol/dm-3) 0.00 12.5 11.25 10.0 8.75 7.50 6.23 5.00 3.75 2.50 1.25 Absorbance 0.00 1.045 1.065 0.874 0.798 0.753 0.648 0.428 0.324 0.212 0.152 4 5 6 1.2 1 0.8 Absorbance 0.6 0.4 0.2 0 0 2 4 6 8 10 12 Concentration of I2 (10-3 mol/dm3) Graph of concentration of iodine against time for the reaction between iodine and propanone Time 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 Concentration of I2 (10-3 mol/dm-3) 9.390 6.110 2.800 1.010 0.849 0.849 0.861 0.861 0.872 0.895 0.906 0.917 14 13.0 14.0 15.0 0.929 0.939 0.939 Graph of concentration of iodine against time for a period of 15 minute 14 12 10 8 Axis Title 6 4 2 0 0 2 4 6 8 10 12 14 Axis Title Graph of concentration of iodine against time for a period of 4 minute 16 14 12 10 8 Axis Title 6 4 2 0 0 0.5 1 1.5 2 Axis Title 2.5 3 3.5 4 4.5 ...
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Chemistry Individual Investigation Yann Perusset 13F

2

To increase the number of particles with enough energy for a successful collision the temperature canbe increased. This concept is again shown in the distribution curve shown above, withT1being thecolder temperature andT2being the warmer. The area under the curve past the E

A

shows thenumber of particles with enough energy to form a successful collision. Basically, reactions go faster athigher temperatures because a larger proportion of the colliding molecules have the minimumactivation enthalpy needed to react.Many factors can affect the overall rate of a reaction, the main factors being concentration,temperature, particle size and the presence of a catalyst. When I come to working out the rateequation and I increase the concentration of one of the reactants it is important to keep all otherfactors the same to determine what effect that particular solution has on the rate without any outsideinfluences. An increase in the concentration of a solution increases the amount of particles within it,the more particles there is, the more likely a successful collision.

Order of reaction, rate constants and rate equations

2+3

Rate Equations and rate constant

With a rate equation, it is possible to see how the concentration of each of the reactant affects therate of a reaction. An example of a simple rate equation is shown below.

Rate=k[A]

x

[B]

y

The total order of a reaction is the sum of the orders of the individual reactants. So for this reaction itwould be the sum of x and y.From the rate equation it is also possible to find out the rate-determining step. From looking at theorder of each of the substances it will tell you the relative number of moles of each substanceinvolved in the rate determining step. For example, assume substance A in the equation above is firstorder, this means that there will be one substance in the rate-determining step. From this, it wouldthen be possible to create a mechanism for the reaction.The rate constant can be calculated by rearranging the rate equation. Below is an example of the rateequation above but rearranged in terms of the rate constant, k:

=

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To obtain a reliable value for the rate the initial rates method would be used (shown below)Once the rate equation is worked out, it can be easily linked to the reaction mechanism by looking atthe rate determining step.

Colourimetery

4

The rate of a reaction is the change in concentration of a reactant or product divided by the timetaken for the change to occur. Therefore to calculate the rate, you have to be able to measure theconcentration of a solution. To do so I shall use the process of Colourimetery. A colorimeter can beused to measure the change in colour of a reaction. It works on the principle that coloured solutions(like iodine that I will be using) absorb certain wavelengths of light. The amount of light that isabsorbed by the solution is known as the absorbance of the solution.The absorbance is proportional to the concentration of the solution used (Abs Conc)Known concentrations of the coloured solution are used to produce a calibration curve which canthen be used to find the concentration of any absorbance value that has that coloured solution withinit.

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