The aim of this experiment is to obtain the rate equation for the reaction between iodine and propanone by determining the order of reaction with respect to each reactant and to the catalyst (hydrogen ions).

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            Date:   14/1/2010

Exp. No.:        9

Title:                The kinetics of the reaction between iodine and propanone in

aqueous solution

Aim:        The aim of this experiment is to obtain the rate equation for the reaction between iodine and propanone by determining the order of reaction with respect to each reactant and to the catalyst (hydrogen ions).

Introduction:  The equation of the reaction is:

I2(aq) + CH3COCH3 (aq)              CH3COCH2I(aq) + H+(aq) + I-(aq)

           

            H+ ions acts as a catalyst in this reaction and the rate equation of the reaction is:

            Rate = k [CH3COCH3]p [I2]q [H+]r

            The rate equation can be found by varying the concentration of each species in turn while keeping the others constant and follow the reaction using a colorimeter. As the intensity of the iodine colour decreases, more light is transmitted through the solution (i.e. the absorbance decreases).

There are three parts to this experiment:

  1. Choosing the right filter for the colorimeter.
  2. Calibrating the colorimeter so that the meter reading can be converted to concentration of iodine.
  3. Obtaining values for the concentration of iodine at intervals of time for a series of experiments with the following sets of conditions:
  1.  Initial [CH3COCH3] varying;  [I2], [H+] constant
  2.  Initial [I2] varying; [CH3COCH3], [H+] constant
  3.  Initial [H+] varying; [CH3COCH3], [I2] constant

Each set of experiment gives the order of reaction with respect to one component. The class was split to 3 groups and each group was responsible for varying each component. My group was responsible for varying the amount of catalyst added [H+].

Apparatus and chemicals:

    0.020 M I2 (in KI(aq)), 2.0M CH3COCH3, 2.0M hydrochloric acid, stopwatch, thermometer, 4 burettes, colorimeter with a set of filters, set of optically matched test tubes to fit colorimeter, distilled water

 

Procedure:

Step

  1. (Choosing the right filter)

The cyan filter was chosen (The complimentary colour of red)

  1. (Drawing the calibration curve)

0.02M I2 solution was added to a burette and distilled water was added to another burette.

  1.  6 test tubes were filled with the following volume of 0.020M I2 solution and distilled water.

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  1. The distilled water in test tube 1 was poured into a tube designed for the colorimeter and was put in the colorimeter and the colorimeter was set zero.
  2. The solution in test tube 2 was poured into a sample tube designed for the colorimeter and was put into the colorimeter and the absorbance of was recorded.
  3. The colorimeter was set zero again by putting the tube with distilled water.
  4. Step 6 was repeated 4 times with solutions in test tube 3-6 and all of the absorbance was recorded. The colorimeter was set zero after using the tube ...

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