Page 240 - Physical chemistry understanding our chemical world

PHASE EQUILIBRIA INVOLVING TWO-COMPONENT SYSTEMS: PARTITION 207

How does a separating funnel work?

Partition as a function of solvent

The operation of a separating funnel depends on partition. A solvent contains some
solute. A different solvent, which is immiscible with the first, contains no compound.
Because the two solvents are immiscible – which means they do
not mix – the separating funnel will show two distinct layers (see Immiscible solutions
Figure 5.15). After shaking the funnel vigorously, and allowing its do not mix. The words
contents to settle, some of the solute will have partitioned between ‘miscible’ and its con-
the two solvents, with some sample passing from the solution into verse ‘immiscible’
the previously pure solvent 1. derive from the Latin
word miscere, meaning
We usually repeat this procedure two or three times during the
‘to mix’.
practice of solvent extraction, and separate the two layers after each
vigorous shake (we call this procedure ‘running off’ the heavier,
lower layer of liquid). Several extractions are needed because K (partition) is usually
quite small, which implies that only a fraction of the solute is removed from the
solution during each partition cycle.

Solvent 1

Meniscus (across which
partition occurs)

Solvent 2

Figure 5.15 A separating funnel is a good example of partition: solute is partitioned between two
immiscible liquids