The System: Ethanol - Acetic Acid - Ethy Acetate - Water
The equilibrium system, ethanol-acetic acid-ethyl acetate-water, is well known. The equation for this equilibrium is:
Equilibrium is established very slowly at room temperature when these four substances are mixed. The rate of reactions (both forward and reverse) can be accelerated by using a catalyst so that the equilibrium can be more rapidly established. 3 M HCl is used in this experiment as a catalyst, and the equilibrium at room temperature should be established in a few days. This means that in order to successfully complete this experiment, a series of combinations of reactants and/or products must be prepared a few days before the actual experiment. The mixtures are allowed to stand at room temperature for a least one week, then aliquots of each mixture are titrated with a standard NaOH solution. The amount of HCl in these mixtures is unchanged since the HCl is only a catalyst The amount of NaOH required in each titration is equivalent to the amount of HCl and the acetic acid acid in the equilibrium mixture. The amount of acetic acid at equilibrium can be calculated easily from the amount of NaOH used in the titration. The amount of acetic acid found is used to calcuate the amounts of the remaining three substances. The equilibrium constant is then calculated by the equation:
The four quantities in the above equation may be replaced by the number of moles of the four substances involved since the volume is constant in each mixture,
Procedure:
Prepare each mixture you are assigned in separate 10 mL screw-capped bottles by using the quantities given in the table below. Deliver the substances into the sample bottles from burets in the following order: (1) HCl, (2) distilled water, (3) acetic acid, (4) ethanol, and (5) ethyl acetate. Close the screw-caps, and mix the contents in the bottles. Shake the contents of the bottles each day to make sure the mixtures remain as homogeneous as possible.
After about two weeks, carefully transfer the contents of each bottle into a 250 mL Erlenmeyer flask. Rinse the bottle three times with 5 mL portions of distilled water, and transfer the washings to the same Erlenmeyer flask. Add two drops of phenolphthalein indicator to each flask, and titrate with standard 1 M NaOH.
Analysis:
From the exact molarity of both the 3 M HCl and the 1 M NaOH and the titration volume, the equilibrium amounts of the four substances in the equilibrium mixture can be determined, and the equilibrium constant evaluated. The average value of Kc with standard deviation should be calculated for the samples titrated by a group, and then the average value of Kc with standard deviation should be calculated for all the values of Kc determined by the class.
Use the following densities in your calculations:
| ethanol, 0.789 g/mL | acetic acid, 1.05 g/mL | ethyl acetate, 0.990 g/mL |
| 3 M HCl, 1.05 g/mL | water, 1.00 g/mL |
| Mixture # | mL 3 M HCl | mL HOAc | mL EtOH | mL EtOAc | mL water |
| 1 | 5 | 0 | 0 | 5 | 0 |
| 2 | 5 | 0 | 0 | 4 | 1 |
| 3 | 5 | 0 | 0 | 3 | 2 |
| 4 | 5 | 0 | 0 | 2 | 3 |
| 5 | 5 | 4 | 1 | 0 | 0 |
| 6 | 5 | 3 | 2 | 0 | 0 |
| 7 | 5 | 2 | 3 | 0 | 0 |
| 8 | 5 | 1 | 4 | 0 | 0 |
| 9 | 5 | 0 | 1 | 4 | 0 |
| 10 | 5 | 0 | 2 | 3 | 0 |
| 11 | 5 | 0 | 3 | 2 | 0 |
| 12 | 5 | 1 | 0 | 4 | 0 |
| 13 | 5 | 2 | 0 | 3 | 0 |
| 14 | 5 | 3 | 0 | 2 | 0 |
| 15 | 5 | 0 | 3 | 1 | 1 |
| 16 | 5 | 0 | 2 | 2 | 1 |
| 17 | 5 | 0 | 1 | 3 | 1 |
| 18 | 5 | 2 | 0 | 2 | 1 |
| 19 | 5 | 1 | 0 | 3 | 1 |
| 20 | 5 | 3 | 1 | 0 | 1 |
| 21 | 5 | 2 | 2 | 0 | 1 |
| 22 | 5 | 1 | 3 | 0 | 1 |
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