Question

(1) Explain the difference between simple distillation and fractional distillation. Which method was more effective at separating the components of your mixtures? How were you able to determine a difference if one was present? Why was there a difference between the two methods if one was present?

(2) Explain in some detail (words and pictures) how each of the three following variables would affect the retention times of a mixture of ethylene glycol and 1-bromobutane

(a) Flow rate of helium carrier gas

(b) Interaction between compounds and stationary phase

Simple distillation: Separate a two-component organic mixture (1:1, tetrahydrofuran and 1-propanol)

Fractional distillation: Separate a two-component organic mixture (1:1 unknown composition)

Answer 1

1)

Simple Distillation

Simple distillation involves the converson of liquid into vapours by heating followed by the condensation of vapours and thus prouced by cooling.

The more volatile liquid distilles first and less volatile liquid( less boiling point) distilles afterwards.

A simple distillation does not include the use of a fractional distillation column.

This Technique purifies an unknown volatile liquid by extracting (and thus isolating it) it from the solution containing a nonvolatile impurity. Isolation can also be done on substances that differ greater than 40-50 deg C

The difference in boiling point properties in between the two Liquid components in order for a simple distillation is Greater than 40-50 deg C. This ensures that the distillate (high volatility) will be separated from the less-volatile solvent.

Example: a mixture of ether(b.p 308K) and toulene(b.p 384K)

Fractional Distillation

If the boiling point of two liquids are very close to each other then the sepration cannot be done by simple distillation due to the reason that at the boiling point of more volatile liquid of the mixture there will be sufficient vapours of the less volatile liquid as well so both the liquid of the mixture will distills together and the sepration is denied.

The fractional distillation different from simple distillation in terms of the presence of a fractional distillation column in fractional distillation.

The Multiple fractions are collected and Method that is able to separate out individual pure liquid components from a mixture containing two or more volatile substances.

The actual purpose of fractionating column is to increase the cooling surface area and to provide the hurdles or obstructions to the ascending vapours and descending liquids.

Example: a mixture of acetone(b.p 329K) and methyl alcohol(b.p 328K)

Also one of the technolgical application of fractionating distillation is to separate the crude oil in petroleum industry into various useful fractions such as kerosine oil,diesel oil,gasoline etc.

The difference between simple and fractional distillation is the number of times that the liquid is vaporized and condensed. Simple distillation condenses the liquid once, so the boiling points of the two liquids must be far apart.

fractional distillation is more efficient. Fractional distillation completes several simple distillations in one apparatus.