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CHEM 343 (1)
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Lecture 2

CHEM 343 Lecture 2: Distillation and Green Chemistry Explanation

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CHEM 343

Green chemistry is the attempt to use resources as efficiently as possible and generate as little waste as necessary. Distillation is a practice in green chemistry, as the purpose of it is to separate liquids as purely as can be done in order to generate very little unusable material. In the case of the latest laboratory technique training, distillation was used to separate ethanol from water. o o Ethanol has a boiling point of 78 C, compared to water’s of 100 C. Because the two boiling points differ by about 25 degrees, they can be separated fairly well using simple distillation. This form of distillation merely heats the mixture and then causes vapor rising from the liquid to condense and enter the receiving container. This method depends fully on the boiling point difference to be enough to separate the liquids by isolating them during the evaporation periods. In the collected data, the ethanol shows signs of having boiled at increasing temperatures, then distilled at a constant rate, which was followed by another increase in temperature as volume increased. It was fairly predictable. However, distillation doesn’t take into consideration that a mixture may contain an azeotrope. An azeotrope is a mixture which boils at a constant rate, though it is not a single compound. Ethanol and water form an azeotrope of 95% ethanol and 5% water. It boils before water does, and is thus a minimum-boiling azeotrope. Fractional distillation allows a chemist to obtain a purer sample, despite the azeotrope. Although, with this particular azeotrope, even fractional distillation should not be able to produce greater than 95% ethanol. Ideally, fractional distillation forms a repetition of simple distillation, but within a column with an increased surface area for condensation to form. Within the column, vapor touches cold surfaces and condenses, passing the heat on to glass beads or whatever one has placed within. The condensed droplets drip back into the distilling flask below. Each time the condensed droplets form, some vapor of the lower-boiling liquid will remain vapor and travel up, while the water falls back down. This increases the concentration of water in the
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