By Cyndie Dallaire Giroux & Veronique Goyette
Table of Contents
For this experiment, we were asking if there was more differences in actual and expected ethanol content between a bottle of wine of good quality and a bottle of lower quality. We have done a quality test to verify if the ethanol content in the two bottles are exactly the same as written on the bottles and then we will try to explain any differences. Our hypothesis was that we would probably have some difference in the quantity of ethanol in the two bottles even if we used a good or a cheap wine. We also thought that the range of difference between the two categories of wine would not vary a lot.
To do this experimentation, we are used the principle of oxidation/reduction titration. In a titration we measure the quantity of one reactant that is required to consume or neutralize all of another reactant and a reduction reaction is the process in which an atom or ion gains electrons. By knowing the volume of solution that we used to titrated another one and by knowing the concentration, were are able to calculate the exact quantity of solution that have been oxidize and then, know the ethanol content of the wine, using the following equation.
1. Standardization of the ferrous ammonium sulfate:
Cr2O72- + 6Fe2+ + 14H+ ------ 2Cr3+ + 6Fe3+ +7H2O
2. Concentration of the ethanol:
2K2Cr2O7 + 3CH3CH2OH + 8H2SO4 -------- 3CH3COOH + 2K2SO4 + 2Cr2(SO4)3 + 11H2O
Before beginning the experiment we have made two important solutions: Ferrous Ammonium Sulfate, Fe(NH4)2(SO4 )4 0.3M , and Potassium Dichromate, K2Cr2O7 , 0.1M .
To do the Ferrous Ammonium Sulfate we dissolved approximately 117.6 g of ferrous ammonium sulfate in a sulfuric acid solution (1M) that have been prepared by dissolving 50 ml of concentrated sulfuric acid in 500 ml of water. Then we added distilled water to obtain exactly 1 L of the solution.
For the potassium dichromate, we dissolved 29.4g of potassium dichromate in 1L of distilled water.
For the standardization of the ferrous ammonium sulfate, we started with 10 ml of potassium dichromate and titrated it in a 250 ml Erlenmeyer flask, with the ferrous ammonium sulfate and labeled the datum. We have done this a second time and labeled again the result.
For the titration we used 0.25g of N-phenylanthranilic acid and dissolved it in about 12 ml of 0.1M NaOH. Then we diluted it to 250 ml of water. This gave us our indicator for the titration.
First, we added 25 ml of potassium dichromate solution in a 100 ml Erlenmeyer flask. Then we added 1 ml of ethanol solution (our wine) to it. This has been placed in a thermostatically controlled bath for 30 minutes at a temperature of 60 C.
Secondly, we added 10 drops of the “redox indicator” to the mixture of potassium dichromate and ethanol and then added 150 ml of distilled water. We titrated this with the ferrous ammonium sulfate until we reached the end point (corresponding to light green color) and noted the result. We have done the same thing with the second wine and noted the result.
Table 1. Standardization of the ferrous ammonium sulfate
|
|
Volume of ferrous ammonium sulfate to
reach the end point (ml) [Fe2+] = 0.22 M |
|
|
Volume of Potassium dichromate |
Trial 1 |
Trial 2 |
|
10 ml |
27.8 ml |
28.1 ml |
Table 2. Titration of the excess of potassium dichromate with the ferrous ammonium sulfate
|
Colors obtained |
Wine #1 (ml) |
Wine #2 (ml) |
|
Light green |
37.7 |
35.8 |
|
Kaki green |
47.5 |
43.5 |
|
Emerald green |
50.0 |
50.2 |
Table 3. Result of the calculation for the ethanol content.
|
|
Wine # 1 |
Wine # 2 |
|
Percentage of ethanol |
9.8 % |
9.1 % |
The hypothesis consisted to compare two different wines (a good quality wine with another one that is cheaper) and first, we said that there would have some differences in the quantity of ethanol in the two bottles of wines. Secondly, we said that the range of difference between the two categories of wine would not vary a lot.
Considering the first part of the hypothesis, the actual ethanol content of the cheaper wine was 11.0% and the one obtained by the experiment was 9.1%. With the good quality wine, the actual ethanol content was 12.3% and the one found in the experiment was 9.8%. In conclusion, the first part of the hypothesis has been verified because we can say that there were some differences in the expected and actual ethanol content in the two bottles.
In the second part of the hypothesis, there was a larger difference in the case of the good quality wine compared to the cheaper one. We can say that the results in the last part were due only to the manipulations and the unclearness of the official procedure paper. In fact, what was expected in it did not correspond to our experimentation; that is to say, in the titration we should have seen a violet-red color just prior to the end-point, which we did not. We can also include some errors in the manipulations: we had an inefficient “redox indicator” because we did not add enough NaOH to dissolve all the N-phenylanthranilic acid. Also, they said in the official procedure paper that the end point will result in a clear dark green but we obtained three different kinds of green and we were not sure which one would be the best to choose for our purpose. As an advertisement for the other teams that will do this experiment, changing the indicator would be a good idea because the actual one did not give a very clear end point.
