Aim:

1

• Aim
• To study the characteristics of ideal and
  non-ideal solutions.
• Learning Outcomes
• At the end of the lesson the students should be
  able to
• Interpret the vapour pressure/composition and the
  boiling point/composition curve for mixtures
  depends on positive or negative deviation.
• Determine the distillate and residue of a
  distillation from the boiling point-composition
  diagram.

Intro
2

• Solutions that exhibit large deviations from
  Raoults law
• There are some solutions that exhibit very large
  deviations from ideality.
• As a result, they cannot be totally separated
  into their components even by fractional
  distillation.

3

• Solutions exhibit a large positive
• deviations from Raoults law
• (Ethanol and Water)
• Solutions of these two substances have a maximum
  in the vapour pressure curve and hence a minimum
  in the boiling point diagram such a solution has
  minimum-boiling azeotrope.

4
The b.p diagram for water-ethanol mixtures (a
minimum-boiling azeotrope solution with ve
deviations)
A
B
5

• Ethanol-water mixtures (obtained by fermentation
  of sugar for example), are rich in water.
• Cannot be separated in a single fractional
  distillation process.
• When a solution of composition A is heated, the
  succession of vaporization and condensation
  finally gives azeotropic mixture as the
  distillate, leaving pure H2O as residue.

6

• When a solution of composition B is heated, the
  succession of vaporization and condensation
  finally gives azeotropic mixture as the
  distillate, leaving pure ethanol as residue.
• Distillate azeotropic mixture
• Residue pure A or pure B

7

• (ii) Solutions exhibit a large negative
• deviations from Raoults law
• (nitric acid and water)
• Solutions with large negative deviations from
  Raoults law have a minimum in the vapour
  pressure curve and hence a maximum in the boiling
  point diagram.
• A solution with such a maximum boiling point is
  called a minimum-boiling point azeotrope.

8
The b.p diagram for nitric acid (a
maximum-boiling azeotrope/solution with -ve
deviations)
Temperature /?C
100
78.5
100 water
100 HNO3
A
B
9

• Fractional distillation is able to concentrate
  the nitric acid.
• When a solution of composition A is heated, the
  succession of vaporization and condensation
  finally gives pure H2O as the distillate, leaving
  azeotropic mixture as residue.

10

• When a solution of composition B is heated, the
  succession of vaporization and condensation
  finally gives pure HNO3 as the distillate,
  leaving azeotropic mixture as residue.
• Distillate pure HNO3 or pure H2O
• Residue azeotropic mixture