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Monday, April 28, 2014

Acid Catalyzed Iodination of Acetone - Physical Chemistry - Lu Le Laboratory


1.     To determine the order of the reaction of iodine-acetone.
2.     To determine the rate constant at an assigned temperature


        Acid catalyzed iodination of acetone is a complex reaction. The rate law for overall reaction cannot be determined from the balanced equation for the reaction but from experiments.
        When an aqueous iodine solution is reacted with acetone in the prescence of an acid, the yellow color slowly fades as the iodine, I2, is consumed. The products of the reaction are iodoacetone and hydrogen iodide. Hydrogen ion is a catalyst for this reaction. The mechanism of the reaction is as follow:

Hydrogen ion participate in the reaction as a catalyst in step on and step two and also be produced as a product in step three. This kind of reaction is called an autocatalysis reaction. The rate equation can be represented as follow
  The reaction progress can be tracked by the determination of the concentration of iodine and triiodide ion.

  For the reaction, the K- =700 and the absorbance of the solution can be represented as follow 
A = A(I3-)+A(I2) = ε(I3-)L[I3-] +ε(I2)L[I2]

When we set the wavelength of the light source of the spectrometer at 565nmthe molar absorbance of I2 and I3- is equal: ε(I3-) = ε(I2)

Absorbance = ε(I3-)L[I3- + I2]

    Since the concentration of acetone and hydrochloric acid is much larger than the concentration of iodine/triiodide ion so we can assume the concentration of acetone and acid as a constant at the beginning of the reaction:

r = k[A]α[I3-]β[H+]δ = k[A]α[H+]δ = constant

    Finally, we can figure out the reaction order and the activation energy of the reaction from Arrhenius equation:

1.     Iodine/KI solution (standardized): 0.02134M
2.     Acetone aqueous: 3.3738M
3.     Hydrochloric acid: 1.436M
4.     Distilled water


1.     Computer

2.     722S Spectrometer

3.     Cuvette
4.     Thermostatic water bath
5.     Pipette
6.     Dropper
7.     Washing bottle


1.     Calibration the spectrometer with distilled water before use.
2.     Turn on the thermostatic water bath and set the temperature at 25.
Put the vessels with distilled water, acetone aqueous, hydrochloric acid, iodine solution in the water bath for at least 10 minutes.

3.     Measurement the εL value of iodine solution:
    Turn on the 722S spectrometer and warm it up for at least 10 minutes. Put the cuvette with d.d. water into the spectrometer as a blank. Pour 25.00mL iodine  solution into a 25mL volumetric flask and dilute to the mark line with distilled water. Rinse the cuvette with the solution for twice, and add the solution to the two-third full of the cuvette, and determine the absorbance with the spectrometer.

4.     Mix the reactants in a volumetric flask as follow and dilute to the mark line then put into the spectrometer:

Iodine solution (mL)
Acetone aqueous (mL)
Hydrochloric acid(mL)

Experimental Record

Table 1. Concentration of Reagents
Iodine/KI solution
0.02134 M
Acetone aqueous
3.3738  M
Hydrochloric acid
1.436   M

Table 2. The εL value
The εL value of the diluted iodine solution (λ=565nm)

Data Process

                First, do linear fitting for each diagram.
Take 30~300s for sample 1.
Take 30~300s for sample 2.

Take 30~300s for sample 3.

Take 30~300s for sample 4.

        Take 30~150s for sample 5.

        Second, figure out the absorbance constant of iodine solution by the equation as follow:
Abs. x constant = Concentration

=> Abs.=0.3636, concentration = (0.02134*2.5/25)=0.002134M
=> constant= 5.869x10-3.

        Third, multiply the constant with each slopes which we get from the figure above and the rates of reactions are as follow:
Table 3. Rate of Reaction
-2.1737 x10-6
-2.4358 x10-6
-4.3071 x10-6
-9.1560 x10-6

        The reaction orders can be found by the calculations as follow:

=>   β= 1.0420

=>   δ= 0.8781

=>   α= -0.0953
        The rate equation can be represented as follow:

        Then the reaction constant k can also be found:
Table 4. Reaction constant k

        Finally the activation energy can be fiqure out from Arrhenius equation:


[1]  傅献彩, 沈文霞, 姚天扬. 物理化学, 上册欧4 . 北京:高等教育出版社, 1990:144.
[2]  清华大学化学系物理化学实验编写组. 物理化学实验. 北京:清华大学出版社, 1991.
[3]  Robert C. Wcast Handbook of Chemistry and Physics. Physics. 58th ed. Ohio: CRC Press, 1977.
[4]  朱文涛. 物理化学. 北京:清华大学出版社,1995.

Tuesday, April 22, 2014

Kinetic Studies on Saponification of Ethyl Acetate by the Conductance Method - Physical Chemistry


1.     To know the characteristics of a second-order reaction by a graphical method.
2.     To determine the effect of temperature on the reaction rate of ethyl acetate with dilute sodium hydroxide.
3.     To be familiarized with the operation of a digital conductometer.


        The saponification of ethyl acetate with sodium hydroxide is a second-order, irreversible reaction which can be represented by the following equation:

         If the initial concentration of the reactants are equal (both a) and that converted concentration is x at reaction time t, then the concentration of ethyl acetate and NaOH is C0-x. Supposing that the reverse reaction can be ignored, the reactant and product concentrations at different time are

t = 0
t = t
C0 - x
C0 - x
t -> ∞
-> 0
-> 0
-> C0
-> C0

        The rate equation for the above second-order reaction can be expressed as

Where k2 is second-order rate constant,  mol-1 L min-1
        The equation can be integrated to give:

        From the concentrations of the reactant and product in the reaction vessel and time of reaction, rate constant k2 can be calculated.

        In this reaction, OH- ion is the most highly conductive species therefore the conductivites of the ethyl acetate and ethyl alcohol may be ignored. Since the reaction solution is dilute aqueous, it can be assumed that sodium acetate is completely ionized. The concentration of Na+ remains invariable before and after reaction. As the reaction time increases, the number of OH- ions decreases continuously, and the conductance of the system declines continuously.

t = 0
к0 = A1C0
t = t
кt = A1(C0 - x) + A2x
t = ∞
к = A2a


Where к0 and кt are the conductivity at beginning and time t, respectly, к is the conductivity at the end of reaction, and A is the proportionality constant. Substituting the equation into below                                              


A plot of 0 - кt)/(кt – к) against t sjould yield a straight line with a slpoe of k2C0 AND k2 can be calculated from the slope. The rate of reaction as characterized by its rate constant k is strongly temperature dependent. This is generally express as the Arrhenius equation:

Where  Ea : activation energy, kJ/mol
             T : the reaction temperature, K
             R : gas constant, J/(mol K)
        From the equation Ea can be obtained based on the determination of kT2 and kT1.                                                                                                                            


1.     NaOH(aq) (0.01852 M, standardized )
2.     NaOAc(aq) (0.00926 M)

3.     Ethyl acetate (A.R.)
4.     Distilled water


1.     Digital conductometer and computer

2.     Platinum electrode

3.     Glass reactor

4.     Volumetric flask
5.     Thermostatic water bath
6.     50-mL test tube
7.     Pipette
8.     Washing ear ball

Measurement of к0 ~ кt
        Add 20-mL NaOH(aq) in the tube 1 and 20-mL ethyl acetate in tube 2. Set up the platinum electrode on the reactor and put the reactor in the thermostatic water bath for at least 10 minutes until the temperature is constant. Turn on the computer and the recorder. Use a washing ear ball to force the solution in tube 1 to remove to tube 2 and quickly mix for 3~5 times. Let the recorder works for about 20 minutes. Raise the temperature high for 3 and repeat the same steps above until the temperature is above 30.

Measurement of к
        Also suck a 50-mL test tube in the thermostatic water bath and hold with 0.00926M NaOAc(aq). After each temperature of measurement of к0 ~ кt , wash the platinum electrode with distilled water and then suck the electrode in to the sodium acetate solution. Record the reading on the conductometer.

Experimental Record

     Raw Data

NaOH(aq): 0.01852M ; Room Temperature.20.0 ; EtOAc(aq): 0.181 mL
Temperature 1 20.08 ; Conductivity of 0.00926M NaOAc(aq): 420 uS/cm

Temperature 2 22.90; Conductivity of 0.00926M NaOAc(aq): 448 uS/cm

Temperature 3 26.30 ; Conductivity of 0.00926M NaOAc(aq): 478 uS/cm


   Take the points after the 100th point

According to the slope of these three diagrams, the k2 can be easily figured out as follow:

-5.8324 x10-4
6.2984 x10-2
-6.8120 x10-4
7.3564 x10-2
-8.2301 x10-4
8.8878 x10-2
Draw a ln(k2)-(1/T) figure and do a linear fitting with these points. The slope of the diagram could be expressed as: slope = -Ea /R

    For the slope = -4863.73, R = 8.314, and then the is Ea 40.52 kJ/mol
To compare with the literature value[6] 39.9 kJ/mol , it is very close.

Ea (experimental)
40.52 kJ/mol
Ea (literature)
39.9  kJ/mol
Percentage error


[1]  傅獻彩, 沈文霞, 姚天揚. 物理化學, 上冊歐4 . 北京:高等教育出版社, 1990:144.
[2]  清華大學化學系物理化學實驗編寫組. 物理化學實驗. 北京:清華大學出版社, 1991.
[3]  Robert C. Wcast Handbook of Chemistry and Physics. Physics. 58th ed. Ohio: CRC Press, 1977.
[4]  朱文濤. 物理化學. 北京:清華大學出版社,1995.
[5]  W. T. Gooch, J. Am. Chem. Soc., 1927, 49 (9), pp 2257–2257
[6]  ADELIO M. MENDES, LUIS M. MADEIRA, FERNAo D. MAGALHAES, J 0513 M. SOUSA. Universidade do Porto - Porto, Portugal