Synthesis of Ethanol - a lab report. they do not change. PDF

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a lab report. they do not change....

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Synthesis of Ethanol and Purification through Simple and Fractional Distillation

Objective: The objective of the lab was to synthesize ethanol through fermentation. Biocatalysts were used along with Pasteur salts to encourage the fermentation process. The goal of the experiment was to increase the ethanol percentage by purifying the fermentation solution through fractional and simple distillation. Procedures and Observations: Procedure Part One: Fermentation Set-up:

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1. Approximately 20 grams of sucrose were placed into a 250mL round bottomed flask. Approximately 100mL and 1.5g of yeast were added to the sucrose. The solution was stirred

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Observations 20.111g of sucrose was weighed out and placed into a 250mL round bottomed flask. The sucrose resembled salt. It was white and gritty. 100mL of water followed 1.519g of yeast was added to the

until all the sugar was dissolved.

 2. 17-18mL of Pasteur’s salts was added to the solution; it was then swirled until all the solutes were dissolved.

3. The flask was capped with a lightly greased cap. This apparatus was then placed into a large beaker that contained paper towels for cushion. 4. A medium-sized test tube was filled halfway with limewater. This was then stabilized in an Erlenmeyer flask. 5. The free end of a rubber tubing was submerged into the limewater. 6. The fermentation set up was placed in sunlight for a week. Part two: Preparation of Distillation Solution 1. Approximately 5g of celite was added to the fermentation mixture. A vacuum filtration was done to collect filtrate.

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sucrose and water. The yeast was brown and smelled like sourdough bread. The substance had a brownish tint (because of the yeast) that resembled polluted ocean water 18mL of Pasteur’s salts was added to the solution This did nothing to the appearance of the solution; the color remained the same

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The limewater was foggy but clear at the same time

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The enzymes in the yeast converted the sugar to ethanol

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5.1141g of celite was weighed out The celite was white and powdery; it resembled flour There was no odor until after the celite was added to the fermentation mixture; smell like spoiled food After filtration, the solution was a yellow color The left-over product on the filtration paper resembled sand

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Part three: Simple Distillation 1. Approximately 90mL of solution was transferred into a 250mL round bottom flask 2. The simple distillation apparatus was set up. All the joints were lightly greased, and a graduated cylinder was used as a receiving flask. Boiling chips were added to the solution to prevent bumping and superheating.

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All the joints were greased to ensure a tight seal and to prevent the joints from locking up The grease was a thick white consistency that was sticky to the touch The heating unit was set to 30˚ but

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was increased to 55˚ to speed up the boiling process The simple distillation process was difficult when it came to stabilizing the apparatus; a lot of trial and error.

3. The solution was distilled at a rate of 1 to 2 drops/sec; the temperature was recorded every 2mL. 4. Approximately 1mL of the simple distillate was pipetted into a 10mL Erlenmeyer flask to calculate the % ethanol. Data: Simple Distillation Volume Distillation (mL)

Temperature (˚C)

2

78.2

4

78.7

6

79.3

8

81.2

10

82.9

12

84.1

14

84.8

Bp range: 78.2 – 84.8˚C Weight of 5mL distillate sample: 4.518g Volume distillate: 14.0 mL Fractional Distillation Volume (mL) 1 2 3 4 5 6 7 8

Temperature (˚C) 76.5 78.0 78.8 79.1 79.7 80.4 80.4 80.6

9 80.9 10 80.9 Bp range: 76.5-80.9˚C Weight of 1mL distillate sample: 0.8221g Volume distillate from 77-80˚C: 10.0mL Volume of distillate from 80-96˚C: 0mL Calculations: Simple Distillation Mass (g)

Volume (mL)

Density (g/mL)

4.518

5.00

0.904

Density:

4.518 g 5.00 mL

% Ethanol Weight 55.0

% Ethanol Volume 62.8

% Ethanol Weight 90.0

% Ethanol Volume 93.3

= 0.904 g/mL Fractional Distillation

Mass (g)

Volume (mL)

Density (g/mL)

0.8221

1

0.8221

Density:

0.8221 g 1mL

Sketches: 

Fermentation

= 0.8221g/mL

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Simple Distillation

Discussion: When preparing ethanol, fermentation is a process where sucrose is converted to carbon dioxide (CO2) and ethyl alcohol (ethanol). This process was carried out by the biocatalysts found in yeast that initiated and increased the rate of the chemical reaction. The addition of Pasteur salts facilitated the formation of ethanol precursors: gluco- and fructo-phosphate. Lime water, a diluted solution of calcium hydroxide, was used to make a closed system. As fermentation occurred, CO2 was produced that traveled through a rubber tubing and bubbled through the lime water. This caused the lime water to turn a milky color. The apparatus was placed in direct sunlight for a week to speed up the enzymes and to allow the solution to ferment properly. As the

fermentation process stopped, the fermentation solution was purified through simple and fractional distillation processes. In the simple distillation set up, the flask that contained the mother liquor was directly connected to a 3-way adapter which was then connected to a thermometer and a condenser. The fractional distillation set up was the same with an exception of a column filled with glass beads. This was placed between the flask containing the mother liquor and the 3-way adapter. The rate of collection in the receiving flask for both distillations was 1 to 2 drops per second. Three fractions were collected for fractional distillation: 77-80˚C, 80-96˚C, and anything above 96˚C; only one fraction was collected for simple distillation: 96-100˚C. The probable composition of the 77-80˚C fraction (in fraction distillation) was mainly ethanol because the boiling point of pure ethanol is within this range. As the temperature of each fraction increases, the amount of ethanol in each distillate decreases due to the ethanol being boiled off and the boiling point of water being reached. This goes for simple distillation as well.

The fractional distillation can further increase the ethanol concentration of the distillate. The column provided an increase in theoretical plates which caused the surface area to increase. This allowed for the separation of the components of the mother liquor to occur. As the mother liquor boiled, the vapor entered the column and condensed upon contact with the beads. Consequently, the compound with the lowest boiling point, ethanol, reached the top of the column and re-condensed and dropped into the distillate. An ethanol-water azeotrope was created due to the miscibility of the two liquids; therefore, making it impossible to completely isolate the ethanol.

The separation of components and the formation of the azeotrope was transpired in the data. The fractional distillation graph contained prominent, abrupt transitions due to the azeotrope distilling at around its boiling point and because of the sharp separation of components. The simple distillation graph did show changes in the amount of distillate collected, but the transitions were not as prominent and abrupt due to the lack of theoretical plates and the poor separation of the components. Post-Lab Questions: 1. An azeotrope is a liquid mixture with a constant boiling point. The boiling point of our ethanol-water azeotrope was approximately 78.2 ˚C with a % composition of about 96% alcohol and about 4% water. The boiling point of our ethanol-water azeotrope was closer to the boiling point of pure ethanol (76-77˚C) than water which has a boiling point of 100˚C. 2. An azeotrope has a constant boiling point but is not a pure liquid; therefore, a constant boiling point does not necessarily imply a pure liquid. 3. The 77-80˚C fraction should contain the highest % volume of ethanol. The probable composition of the 96˚C fraction is water. 4. A minimum-boiling azeotrope is a liquid mixture that has a lower boiling point than its individual parts. A maximum boiling azeotrope is a liquid mixture that has a higher boiling point that is individual parts. The ethanol-water is a minimum-boiling azeotrope. Bonus Questions

1. Green chemistry is an area of chemistry that focuses on reducing the use of hazardous substances. This lab was “green” because of the lack of hazardous substances used or created in the lab....