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The Partition Coefficient (Kpc)

Partition coefficients concern immiscible liquids. Immiscible liquids include things like oil and water.

Immiscible liquids

Immiscible liquids

  • When you mix immiscible liquids, they form two distinct layers.
    • Think about oil on top of water, or an unshaken bottle of your favourite vinaigrette.
  • If you then add a molecule that is soluble in liquids, the molecule will distribute between the two liquids. The distribution depends on which liquid the added molecule is more soluble in.
  • Eventually, a dynamic equilibrium is set up.
Example

Example

  • Water and oil are immiscible. Substance Y dissolves in both oil and water.
  • We can write an equation for the dissolution of substance Y:
    • Ydissolved in water ⇌ Ysolution in oil
  • To calculate Kpc, we can set up an equilbrium expression:
    • Kpc = [Yin oil][Yin water]\Large\frac {[Y_{in \ oil}]}{[Y_{in \ water}]}
  • The same general principles that apply to other equilibrium constants apply to Kpc.
Units

Units

  • The concentration for Kpc expressions is normally given in g cm-3.
  • If there were 5 g cm-3 of substance Y in oil, and 10 g cm-3 in water, the Kpc would be:
    • Kpc = [Yin oil][Yin water]\Large\frac {[Y_{in \ oil}]}{[Y_{in \ water}]} = 5 / 10 = 0.5.
Jump to other topics
1

Physical Chemistry

1.1

Atoms, Molecules & Stoichiometry

1.2

Atomic Structure

1.3

Chemical Bonding

1.4

States of Matter

1.5

Chemical Energetics

1.6

Electrochemistry

1.7

Equilibria

1.8

Partition Coefficient

1.9

Reaction Kinetics

2

Inorganic Chemistry

3

Organic Chemistry & Analysis

3.1

Introduction to Organic Chemistry

3.2

Hydrocarbons

3.3

Halogen Derivatives

3.4

Hydroxy Compounds

3.5

Carbonyl Compounds

3.6

Carboxylic Acids & Derivatives

3.7

Nitrogen Compounds

3.8

Polymerisation

3.9

Analytical Techniques

3.10

Organic Synthesis

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