Re: Chem lab report 18 (To effect a partial separation of ethanol from ethanol-water mixture) -- LukeC��Q�װ�

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Subject:

Re: Chem lab report 18 (To effect a partial separation of ethanol from ethanol-water mixture)

Author:
LukeC

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Date Posted: 05:37:56 11/14/02 Thu
In reply to: n/a 's message, "Chem lab report 18 (To effect a partial separation of ethanol from ethanol-water mixture)" on 05:34:28 11/14/02 Thu

1. Water-ethanol mixture is a non-ideal solution; when ethanol and water are mixed together, heat is absorbed and the total volume is greater than that of the individual components. This suggests that there has been a disruption of the intermolecular bonds present in one component when the liquids are mixed. Ethanol interferes with the strong hydrogen bonding in the water. Since the intermolecular bonding has been decreased each of the components will vaporize more readily, (lower boiling point), and the vapor pressure will be increased. There is a slight increase in volume when the liquids are mixed and since bonds are broken an endothermic enthalpy change is observed, thus there is a positive derivation.

2. To separate ethanol from water-ethanol mixture completely, we can carry out three methods.

By distillation with a third component:
First added benzene to the ethanol-water allotrope, distillations first yield a ternary azeotropic mixture of ethanol-water-benzene, then a binary azeotropic mixture of ethanol-benzene, and finally the pure ethanol.

By adsorption:
Use silica gel or charcoal to adsorb the water.

By chemical reaction:
The water can be removed by standing over anhydrous calcium oxide for several hours, followed by filtration and then distillation.

By solvent extraction:
Adding ether to water-ethanol, then separate the water with a separating funnel. Repeat it by adding ether and separate water. (Boiling point of ethanol is 78.5C, boiling point of ether is 35C)

Conclusion:

The experiment shows the boiling point range of the distillate increase, more water distill out.

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