Equilibria between different phases
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Equilibria between different phases. Advanced Higher Unit 2b(ii). Separating Funnel. Separates immiscible liquids with different densities Usually water, plus an organic solvent (ether, chloroform). [solute](organic). K =. [solute](aq). Partition Coefficient.

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Equilibria between different phases

Equilibria between different phases

Advanced Higher

Unit 2b(ii)


Separating funnel

Separating Funnel

  • Separates immiscible liquids with different densities

  • Usually water, plus an organic solvent (ether, chloroform)


Partition coefficient

[solute](organic)

K =

[solute](aq)

Partition Coefficient

  • When a solute is added to two such immiscible liquids, some will dissolve in each layer

  • The distribution will not be even

  • Ratio of distributed called PARTITION COEFFICIENT


Solvent extraction

Solvent extraction

  • Partition coefficient is used in solvent extraction and for purification

  • For example, with an impure carboxylic acid, the acid will dissolve in ether but impurities will not


Calculation

Calculation

Consider the following partition coefficient of an organic acid:

[acid](ether)

K =

= 5

[acid](aq)

If 10g of acid is dissolved in 100ml of water and 100ml ether, the quantity of acid which can be extracted can be calculated...


Equilibria between different phases

x / 100

= 5

(10 – x) / 100

x

= 5

(10 – x)

x

= 50 – 5x

6x

= 50

x

= 8.3 g

[acid](ether)

K =

= 5

[acid](aq)

Concentration organic acid (ether) = x / 100

Concentration organic acid (aq) = (10 – x) / 100


An alternative method

An alternative method

  • Repeat the previous calculation, but this time for using 100 ml water and 50 ml ether for a first extraction, then repeating with another 50 ml ether for a second extraction


Equilibria between different phases

[acid](ether)

K =

= 5

[acid](aq)

x / 50

= 5

(10 – x) / 100

Concentration organic acid (ether) = x / 50

Concentration organic acid (aq) = (10 – x) / 100

x

= 5

(10 – x) / 100

50

x

= 50 – 5x / 100

50

100x

= 50 – 5x

50

2x

= 50 – 5x

7x

= 50

x

= 7.14 g


Equilibria between different phases

[acid](ether)

K =

= 5

[acid](aq)

x / 50

= 5

(2.86 – x) / 100

Concentration organic acid (ether) = x / 50

Concentration organic acid (aq) = (2.86 – x) / 100

x

= 5

(2.86 – x) / 100

50

x

= 14.3 – 5x / 100

50

100x

= 14.3 – 5x

50

2x

= 14.3 – 5x

Total extracted:

7.14 + 2.04 = 9.18g

7x

= 14.3

x

= 2.04 g


Chromatography

Chromatography

  • Method of separation which depends on the partition of substances between two phases

  • One is mobile, the other is stationary

    • Stationary phase – depends on type of chromatography

      • Paper

      • Thin layer

      • Column

      • Gas/liquid

      • High performance liquid


Equilibria between different phases

Task

  • Each group take one of the chromatography types and prepare a one page notes sheet for the class and for the Think-chemistry website


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