Equilibria between different phases

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# Equilibria between different phases - PowerPoint PPT Presentation

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

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
• 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
• 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

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...

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
• 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
[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

[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
• 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