Define partition coefficient ( K pc ) .

A partition coefficient ( K pc ) is the ratio of the concentration of a solute in an organic solvent to its concentration in water (or vice versa), at equilibrium and at a specified temperature.

State the equilibrium expression for the partition coefficient of methylamine (CH 3 NH 2 ) distributed between an organic solvent and water.

CH 3 NH 2 (aq) ⇌ CH 3 NH 2 (organic solvent) K pc = [CH 3 NH 2 (organic)] / [CH 3 NH 2 (aq)]

True or False? When K pc is greater than 1, the solute is more soluble in the organic solvent than in water.

True. K pc > 1 means [solute in organic] > [solute in water], so the solute has a higher solubility in the organic solvent.

The partition coefficient depends on the .......... of the solute in each solvent, which is determined by the strength of .......... forces between solute and solvent molecules.

The partition coefficient depends on the solubility of the solute in each solvent, which is determined by the strength of intermolecular forces between solute and solvent molecules.

Explain why ammonia has a lower partition coefficient (organic / water) than expected from its molecular mass alone.

Ammonia and water are both polar and form hydrogen bonds with each other. Ammonia forms only weaker permanent dipole-induced dipole interactions with non-polar organic solvents. The stronger hydrogen bonding makes ammonia more soluble in water, lowering K pc .

True or False? The partition coefficient changes with temperature.

True. K pc depends on the solubilities of the solute in each solvent, which are temperature-dependent. A change in temperature alters the equilibrium position and therefore the value of K pc .

In a partition coefficient calculation using titration, why is only part of the aqueous layer titrated rather than all of it?

A measured aliquot (e.g. 50.0 cm 3 ) is titrated for precision and practicality. The moles found in that aliquot are then scaled up proportionally to find the total moles of solute in the full aqueous layer.

Define immiscible solvents .

Immiscible solvents are two liquids that do not mix and form two distinct layers when combined, such as water and an organic solvent like hexane. A solute can distribute between both layers, establishing a partition equilibrium.

If K pc (organic / water) 1, it is more soluble in .......... .

If K pc (organic / water) 1, it is more soluble in the organic solvent .

A LevelChemistryCambridge (CIE)Flashcards25. EquilibriaPartition Coefficients

Partition Coefficients (Cambridge (CIE) A Level Chemistry): Flashcards

Exam code: 9701

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Define partition coefficient (K_pc).

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Define partition coefficient (K_pc).
A partition coefficient (K_pc) is the ratio of the concentration of a solute in an organic solvent to its concentration in water (or vice versa), at equilibrium and at a specified temperature.
State the equilibrium expression for the partition coefficient of methylamine (CH₃NH₂) distributed between an organic solvent and water.
CH₃NH₂ (aq) ⇌ CH₃NH₂ (organic solvent)
K_pc = [CH₃NH₂(organic)] / [CH₃NH₂(aq)]
True or False?
When K_pc is greater than 1, the solute is more soluble in the organic solvent than in water.
True.
K_pc > 1 means [solute in organic] > [solute in water], so the solute has a higher solubility in the organic solvent.
The partition coefficient depends on the .......... of the solute in each solvent, which is determined by the strength of .......... forces between solute and solvent molecules.
The partition coefficient depends on the solubility of the solute in each solvent, which is determined by the strength of intermolecular forces between solute and solvent molecules.
Explain why ammonia has a lower partition coefficient (organic / water) than expected from its molecular mass alone.
Ammonia and water are both polar and form hydrogen bonds with each other. Ammonia forms only weaker permanent dipole-induced dipole interactions with non-polar organic solvents. The stronger hydrogen bonding makes ammonia more soluble in water, lowering K_pc.
True or False?
The partition coefficient changes with temperature.
True.
K_pc depends on the solubilities of the solute in each solvent, which are temperature-dependent. A change in temperature alters the equilibrium position and therefore the value of K_pc.
In a partition coefficient calculation using titration, why is only part of the aqueous layer titrated rather than all of it?
A measured aliquot (e.g. 50.0 cm³) is titrated for precision and practicality. The moles found in that aliquot are then scaled up proportionally to find the total moles of solute in the full aqueous layer.
Define immiscible solvents.
Immiscible solvents are two liquids that do not mix and form two distinct layers when combined, such as water and an organic solvent like hexane. A solute can distribute between both layers, establishing a partition equilibrium.
If K_pc (organic / water) < 1, the solute is more soluble in .......... . If K_pc > 1, it is more soluble in .......... .
If K_pc (organic / water) < 1, the solute is more soluble in water. If K_pc > 1, it is more soluble in the organic solvent.

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