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Biosynthesis of Ethanol from Sucrose

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Ethanol can be created using two methods: acid catalysed hydration of ethylene and through fermentation of sucrose. The purpose of this experiment was to use fermentation to produce ethanol from commercial sucrose (store-bought sugar), using fractional distillation of the fermented solution. The percent ethanol in the fermented solution was then calculated. Mechanism:

Mass of conical vial
10.36 g
Mass of conical vial with distillate
11.17 g
Mass of distillate (mass of vial-mass of vial with distillate) 11.17 g – 10.36 g = 0.81 g
Volume of distillate using automatic pipet
1 mL
Density of distillate (mass of distillate/volume of distillate)

Percent composition by weight of ethanol using table on page 006 ~90%
Percent composition by volume of ethanol using table on page 006 ~93.3%

Percent Yield:
Theoretical Yield:
1 sucrose→4 ethanol

100 % weight and volume percent EtOH
Experimental Yield:
(from table): 93.3% EtOH by volume.
Percent Yield:

The percent yield of ethanol from sucrose was successfully high, at 93.3 %. The final mass of the distillate obtained after fermentation and the fractional distillation process was 0.81g. The distillate was collected when the temperature reached approximately 50-70°C. The amount of ethanol that should have been produced was 13.66 ml, had the entire distillate (over 100 ml) been distilled fractionally . The density of the distillate obtained was 0.81 g/mL; therefore, the percent ethanol by weight was approximately 90%. The distillate contained mostly ethanol, but also contained water because due to the azeotropic mixture water and ethanol mix to produce, consisting of 95% ethanol and 5% water by weight. This experiment was a success due to the high percent yield of ethanol from the fermentation of sugar.

Errors introduced to this lab consisted of using unclean glassware that may have produced side reactions, inefficient temperature regulation during fermentation, oxygen in the fermentation process resulting in unwanted byproducts, and inconsistent distillation resulting in water in the final distillate. Questions:

1. 187 proof
2. Ethanol boils at 78.4 °C, water boils at 100 °C, but the azeotrope, consisting of 95.63% ethanol and 4.37% water boils at 78.2 °C, which is lower than either of its constituents. Hence, if the distillate was set to boil at 78.2°, a perfect azeotropic mixture would be produced. 3. One method described in literature was for 95% ethanol to be refluxed with freshly ignited CaO (250g/L) for some time before distilling, to expel moisture through a dehydration reaction. Another method would be to fractionally distil the distillate further, but at 78.4°C (bp for ethanol) in order to ensure that solely the ethanol would be collected.

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