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Organic chem lab exam 1

SIMPLE AND FRACTIONAL DISTILLATION
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SIMPLE AND FRACTIONAL DISTILLATION
4. If heat is supplied to the stillpot too rapidly, the ability to separate two liquids by fractional distillation may be drastically reduced. In terms of the theory of distillation presented in the discussion, explain why this is so.
A successful fractional distillation depends upon maintaining a temperature gradient within the column. Ideally, the temperature at the bottom of the column should be similar to the boiling temperature of the solution in the pot, and it should decrease continuously in the column until it reaches the boiling point of the more volatile component at the top of the column.If the distillation flask is heated too rapidly, the whole column will heat up almost uniformly and eliminate the desired temperature gradient. The result will be minimal fractionation and separation of the components.
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5. Explain why the column of a fractional distillation apparatus should be aligned as near to the vertical as possible.
The success of a fractional distillation requires that the material passing through the column condense and vaporize within the column. The column must be as vertical as possible to maximize contact with the column packing and the condensate as it passes back down the column. If the condensate runs down the side of the column rather than through the packing, there will be minimum contact between liquid and vapor.
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6. Explain the role of the boiling chips or magnetic stirring bar normally added to a liquid that is to be heated to boiling.
Boiling chips (or magnetic stirring) are added to ensure smooth boiling of the liquid and reduce the possibility of bumping in the stillpot by providing a surface for forming small bubbles of air. Their absence fosters superheating of the liquid and severe bumping.
The top of the mercury bulb of the thermometer placed at the head of a distillation apparatus should be adjacent to the exit opening to condenser. Explain the effect on the observed temperature if the bulb is place below the opening to the condenser or above the opening.
If the mercury bulb is too low, high temperature readings are observed because the bulb is in contact with liquid and vapor having a higher temperature than the vapor entering the condenser.
b. If the mercury bulb is too high, low temperature readings are observed, because the bulb is not in full contact with the vapor entering the condenser.
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