Liquid-liquid Extraction

Question 1

Describe liquid-liquid

Answer 1

• useful
method to separate components
(compounds) of a mixture

• Extractions use two immiscible
phases to separate a solute
from one phase into the other.

• The distribution of a solute
between two phases is an
equilibrium condition described
by partition theory.

Example: boiling tea leaves in water
extracts the tannins,
theobromine, and caffeine out
of the leaves and into the water.

Question 2

Elemental analysis generally required?

Answer 2

It requires fairly simple (not
necessarily easy) sample
preparation. Solids are usually
dissolved or digested in caustic
solution and liquids are sometimes
extracted to separate the analyte
from interferences.

• Real-world samples can be very
complicated matrices that require
careful extraction procedures to
obtain the analyte(s) in a form
that can be analyzed.

Question 3

What is Partition Coefficient, Kp/
Distribution Coefficient, Kd?

Answer 3

▪When a compound is shaken in a separatory funnel with two immiscible solvents,
the compound will distribute itself between the two solvents
▪Normally one solvent is water and the other solvent is a water-immiscible organic
solvent.
▪Most organic compounds are more soluble in organic solvents, while some organic
compounds are more soluble in water.

At a certain temperature, the ratio of
concentrations of a solute in each solvent is
always constant. And this ratio is called the
distribution coefficient, Kd.

It is more efficient to carry out
two extractions with 1/2 volume
of extraction solvent than one
large volume!

The greater the number of small
extractions, the greater the quantity
of solute removed. However for
maximum efficiency the rule of thumb
is to extract three times with 1/3
volume