Lab Report 3 - Tatum Kroon

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University of Louisville *

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Chemistry

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Feb 20, 2024

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Data Simple distillation Weight Erlenmeyer flask (g) Weight flask + 1.00mL (g) Volume (mL) 1mL weight (g) Density (g/mL) % Ethanol weight % Ethanol volume 16.1339 17.0619 1.00 0.9280 0.9280 45.0 52.7 Fractional distillation (77 – 80 C) Weight Erlenmeyer flask (g) Weight flask + 1.00mL (g) Volume (L) 1mL Weight (g) Density (g/mL) % Ethanol weight % Ethanol volume 16.1478 16.9653 1.00 0.8087 0.8087 93.0 95.4 Fractional distillation (80 – 96 C) Weight Erlenmeyer flask (g) Weight flask + 1.00mL (g) Volume (L) 1mL Weight (g) Density (g/mL) % Ethanol weight % Ethanol volume 16.1268 16.9488 1.00 0.8220 0.8220 90.0 93.3 Fractional distillation (above 96 C) Weight Erlenmeyer flask (g) Weight flask + 1.00mL (g) Volume (L) 1mL Weight (g) Density (g/mL) % Ethanol weight % Ethanol volume 16.1281 17.0536 1.00 0.9255 0.9255 45.0 52.7 Simple distillation Total Volume (mL) Temperature (C) 0.5 83 1.0 86 1.5 87 2.0 87 2.5 88

3.0 89 3.5 90 4.0 90 4.5 90.5 5.0 91 5.5 91 6.0 92 6.5 93 7.0 93 7.5 93 8.0 94 8.5 94 9.0 94 9.5 96 10.0 97 10.5 97 11.0 97.5 11.5 97.5 12.0 98 12.5 98 13.0 99 13.5 99 14.0 99 14.5 99 15.0 99 15.5 100 Fractional Distillation Total Volume (mL) Temperature © 0.5 75 1.0 75 1.5 75 2.0 76 2.5 76 3.0 77 3.5 78 3.5 80 4.5 81 4.6 82 4.8 83 4.85 84

4.9 85 5.0 86 5.1 87 5.6 88 5.8 89 6.0 90 6.1 91 6.2 92 6.3 93 6.4 94 6.5 95 6.6 97 7.6 98 8.1 99 9.0 100 Conclusion/Discussion In this lab, fermentation, and various distillation techniques, which included simple and fractional distillation, were demonstrated to produce ethanol. Along with these techniques, basic laboratory skills, such as vacuum filtration and observational skills were used to determine and estimate the density and percent ethanol by weight and volume of each distillate. Fermentation is a metabolic process in which the enzymes in yeast convert sugar into ethanol. Yeast, a microorganism, is used in alcoholic fermentation and consumes the sugar in our fermentation set-up. Invertase and zymase, enzymes of this yeast, break down the sucrose in glucose and fructose (invertase), and then into ethanol and carbon dioxide (zymase). Along with this, the added Pasteur’s salt solution helped aid the formation of the glucose-phosphates and fructose-phosphates. With carbon dioxide as a byproduct, a limewater airlock was used to provide carbon dioxide a way out without it escaping into the air thus preventing a reaction with atmospheric oxygen. Once this metabolic process was allowed to rest for a week, the solution which previously contained mostly sugar, now contained ethanol. Even though both simple and fractional distillation are used to separate liquids, there are some differences. Simple distillation is used to separate two liquids that boil below 150 C. The boiling points of the liquids need to be 25 C apart from each other. Fractional distillation can be used to separate liquids that are soluble in one another, and the boiling points are less than 25 C apart from each other. A fractionating column is used in this setup to provide multiple fractions. The vapor of the mixture moves into this column containing glass beads that provide a large surface area for the vapor to condense. Because of the large surface area, this process will repeat itself multiple times in fractions, enhancing the separation, and is therefore the preferred distillation method compared to simple distillation. In the end, three fractions were collected on a range of temperatures (77-80 C, 80-96 C, >94 C). Even though fractional distillation can be a very effective technique to separate two liquids, there are cases in which a mixture cannot be fully separated by either simple or

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fractional distillation because it has a constant boiling point. This can be referred to as an azeotrope. The most well-known azeotrope is the ethanol-water azeotrope. Once this mixture reaches a composition of 95.6% ethanol and 4.4% water, it boils at a constant temperature and will continue to condense and enter the vapor phase repeatedly, which makes it impossible to recover more than 96% ethanol. This is also why obtaining 100% ethanol by weight or volume is impossible. In the fractional distillation, three fractions were obtained as mentioned previously. The most likely composition of the first fraction (77-80 C) was mainly ethanol because the literature boiling point of ethanol (78 C) falls within this range. As the temperature increased, the amount of ethanol also decreased. The reason behind this is that the ethanol is most likely boiled off and the boiling point for water (100 C) is reached. Since simple distillation only has one fraction, it is less pure because the distillate over a broader temperature range (83-100 C) is collected. The density of both the simple distillation distillate and the three fractions of the fractional distillation was obtained by weighing 1.00mL and calculating the density by dividing the weight by the volume. Once the density was obtained, it was used to estimate the percentage volume and weight with the use of a table provided to us. The density of the simple distillation, 0.9280 g/mL resulted in an estimated ethanol percentage of 45.0% weight and 52.7% volume. The fractional distillation resulted in 3 different results: 77- 80 C density was 0.8087 with a 93.0% weight and 95.6% volume, 80-96 C density of 0.8220, with a 90.0% weight and 93.3% volume, and lastly 96 C and above with a density of 0.9255 and % weight and volume of 45.0% and 52.7%. These results also support that the first fraction (77- 80 C) consisted mostly of ethanol as predicted above. Comparing these results also shows that fractional distillation is a better way to successfully separate two liquids because the percentages of volume and weight of the simple distillation were significantly lower than the 77-80 C of the fractional distillation (45.0 and 52.7% compared to 93.0 and 95.4%). Differences can also be noted in the data collection of the total volume compared to the temperature even though data from both distillation techniques were collected the same way. Temperature was recorded every few mL of distillate collected, and two graphs were made based on those results. In the simple distillation graph, there was no clear increase shown which means that the transitions were not as abrupt as in the fractional distillation graph. This is most likely due to the lack of theoretical plates. In comparison to the fractional distillation graph, this one has clear transitions between temperatures and the amount of distillate collected in each fraction. This shows that there is a sharper separation of liquids compared to the simple distillation, where there was only a constant line on the graph with no clear transitions. All these results support the idea that fractional distillation is a more effective method to separate two liquids compared to simple distillation. Post Lab Questions 1. Explain the following statement: A pure liquid has a constant boiling point, but a constant boiling point does not necessarily imply a pure liquid. A constant boiling point does not necessarily imply a pure liquid because it is also possible that the constant boiling point is a result of an azeotrope; a mixture with a constant boiling point.

2. After fermentation, what is the precipitate in the Ca(OH)2 solution? Write the balanced equation. CO2(g) +Ca(OH)2 (aq)  CaCO3 (s) +H2O (l) Precipitate = CaCO3 3. Why is it impossible for 100% pure ethanol to be obtained from fractional distillation of the fermentation mixture? Water and ethanol form an azeotrope, a mixture consisting of 95.6% ethanol and 4.4% water, it boils at a constant temperature and will continue to condense and enter the vapor phase repeatedly, which makes it impossible to recover more than 96% ethanol. This is also why obtaining 100% ethanol by weight or volume is impossible.