STPM Chemistry Form 6 Notes – Phase Equilibrium (Part 4)

by BerryBerryTeacher

in Berry Reference (Notes)

Distillation process is simply a process of separating mixtures (such as crude petroleum or other mixtures) based on the variation in the volatilities of the components in the mixtures, usually done in high temperature conditions. This Part 4 of Berry Berry Easy‘s short notes on Phase Equilibrium for STPM Form 6 Chemistry attempts to explain the different distillation relevant to STPM Chemistry.

Although common distillation includes simple distillation, fractional distillation, steam distillation, vacuum distillation, air-sensitive vacuum distillation, short path distillation, reactive distillation and extractive distillation, this post will only address the fractional and vacuum version of the process.

[Tips: It should be noted that although distillation is just a simple separation process physically, students will typically misclassify it as a chemical process.]

STPM Chemistry Form 6 Notes – Phase Equilibrium (Part 4)

Distillation Process

Fractional Distillation

Fractional Distillation

Fractional Distillation

  • Distillation is used to remove a liquid from a solution.
  • Fractional distillation – a series of evaporation and condensation cycles.
  • The distilling column / fractionating column has an additional surface area = pack with an inert material (glass beads) or short pieces of glass tubing or increase the length of the column.
  • Increase the surface area of the distilling column / fractionating column is to purify the product by increasing the number of evaporation and condensation cycle / process of vaporization-condensation.
  • Distillation flask = richer in the less volatile component
  • Distillate / Receiving flask = richer in the more volatile component (lower boiling point component in the mixture)
  • Porcelain chips are used to prevent bumping in the distillation flask.

Example:

Which of the following distillations results in the purest product?

A Benzene (b.p. = 80˚C) from 2,3-dimethylbutane (b.p. = 58˚C)
B Diethyl ether (b.p. = 35˚C) from tetrahydofuran (b.p. = 67˚C)
C Heptane (b.p. = 98˚C) from hexane (b.p. = 69˚C)
D Methanol (b.p. = 56˚C) from ethanol (b.p. = 78˚C)

Solution:

The distillation that generates the purest product is the one with the greatest vapour pressure ratio of more volatile component to less volatile component. The greatest ratio is found in the pair of compounds that has the biggest difference in boiling points.

Answer: B

Vacuum Distillation / Distillation under Reduced Pressure

  • Reduce the atmospheric pressure results a compound to boil easily.
  • Boiling point of components has been reduced.
  • It is used when a compound has an extremely high boiling point / has a decomposition temperature lower than its normal boiling point.
  • Disadvantages: danger of implosion and difficult to control bumping because it occurs vigorously and impurities (low boiling point) may be distillated over.

This is the end of Part 4 of Berry Berry Easy‘s short notes on Phase Equilibrium for STPM Form 6 Chemistry. Do return for Part 5 of this series of notes.

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