STPM Chemistry Form 6 Notes – Phase Equilibrium (Part 9)

by BerryBerryTeacher

in Berry Reference (Notes)

Continuing from Part 3,5 and 6 of Berry Berry Easy‘s short notes on Phase Equilibrium for STPM Chemistry Form 6 students, this Part 9 in the series will also be focused on ideal solutions and non-ideal solutions and miscibility. To remind students who missed out on the previous parts, ideal solution and non-ideal solution differs in intermolecular forces of attraction, volume change and enthalpy change. Miscibility simply means the ability of molecules to dissolve in other molecules. So do read on the previous posts before heading on the following post on ideal solution (miscible liquids), non-ideal solution (miscible liquids) and immiscible liquids.

[Tips: In event that students forget the concept of ideal solution, you can just recall its parallel in ideal gases in terms of the thermodynamic properties. Ideal solution is also frequently known as ideal mixture.]

STPM Chemistry Form 6 Notes – Phase Equilibrium (Part 9)

Fractional Distillation

Fractional Distillation

Ideal Solution: Miscible Liquids

Method: Fractional Distillation

  • Boiling point – composition diagram for a mixture (A and B)
  • First distillate: Either one of the pure liquid (A) with lower boiling point / more volatile component
  • Residual / Second distillate: pure liquid (B) with higher boiling point

Non-ideal Solution: Miscible Liquids

Method: Fractional Distillation

  • Boiling point – composition diagram for a mixture

I) Positive deviation

  • Minimum boiling point
  • First distillate: Azeotrop
  • Residual / Second distillate: Either one of the pure liquid
  • Example: ethanol-water system

II) Negative deviation

  • Maximum boiling point
  • First distillate: Either one of the pure liquid
  • Residual / Second distillate: Azeotrope
  • Example: trichloromethane-ethanol system

Sketch graph:

Remember three points (SAL):

  • S = Shape must be correct
  • A = Axes must be with correct unit (if given)
  • L = Label the graph (vapor and liquid or reactants and products or azeotrope)

Immiscible Liquids

Method: Steam Distillation (used to purify an organic liquids which has a high boiling point and decomposes at temperatures near its normal boiling point

Three important points for the steam distillation to be carried out:

  • Immiscible with water
  • High molecular mass
  • High vapour pressure at about 100˚C

This marks the end of Part 9 of Berry Berry Easy notes on Phase Equilibrium for STPM Chemistry Form 6 students. The next part, final part in the series will be on chromatography.

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