Illustrated Guide to Home Chemistry Experiments

Chapter 6 Laboratory: Separating Mixtures 105

LABORATORY 6 .4:

SoLvENT ExTRACTIoN

Solvent extraction, also called liquid-liquid

extraction or partitioning, is a procedure

used to separate compounds based on their

solubility in two immiscible liquids—usually

water and an organic solvent. During solvent

extraction, one or more of the solutes in one of

the liquid phases migrates to the other liquid

phase. The two liquid phases are then physically

separated and the desired product is isolated

from the phase that contains it.

RIREEqU d EqUIpmENT ANd SUppLIES

£ goggles, gloves, and protective clothing

£ test tube with solid stopper

£ test tube rack

£ eyedropper

£ watch glass

£ Lugol’s solution (1 mL)

£ lighter fluid (~2 mL)

£ tap water

SBSTITUTIU oNS ANd modIfICATIoNS

• You may substitute a Petri dish, small beaker, or
  saucer for the watch glass.


• You may substitute tincture of iodine for the Lugol’s
  solution. Tincture of iodine is a solution of iodine in
  ethanol, so using it means that you’re doing a simple
  transfer of iodine from one layer to another rather
  than a separation of the iodine and potassium iodide
  present in Lugol’s solution. Still, the principle can be
  illustrated just as well with tincture of iodine.


• You may substitute gasoline, paint thinner, or any
  other organic solvent that is not miscible with water
  for the lighter fluid.

Solvent extraction is one of the most commonly used laboratory
purification methods, particularly in organic chemistry labs.
Solvent extractions done in chemistry labs are usually small-
scale, batch-mode operations using a separatory funnel. Solvent
extraction is also widely used in industrial operations. Some
industrial applications use batch-mode extraction, albeit usually
on a much larger scale than laboratory solvent extractions. Other
industrial applications use continuous-mode solvent extractions,
often on a gigantic scale, where the two solvents are continuously
added to and removed from a large reaction vessel.

In some solvent extractions, the desired product migrates from
the original liquid phase to the second liquid phase. In other
solvent extractions, impurities migrate from the original liquid
phase to the second liquid phase, leaving the product in the
original liquid phase. The phase that contains the desired product
is called the product layer. The phase that contains impurities,
excess reactants, and other undesirable compounds is called the
waste layer. Many first-year organic chemistry students come to
grief by discarding what they think is the waste layer, only to learn
later that they actually discarded the product layer.

In this laboratory, we’ll use solvent extraction to isolate the iodine
present in Lugol’s solution, an aqueous solution of iodine and
potassium iodide.

dR. pAUL joNES CommENTS:

Maybe you’re relying on them learning the hard way, which

to be honest really is the only way to learn this lesson, but

I like to explicitly tell students not to throw anything away

until they have gotten the product they want/expect. But,

yes, no one listens. Alas, the life of a teacher. They think

you’re an idiot as long as you’re in their presence and only

after they’re miles and years away do they realize you

weren’t a boob.