to settle, and the aqueous layer is once again drained off. This is done in order to extract as much of
the isobutyric acid from the ether layer as possible because it does not completely transfer with the
first extraction. Multiple extractions with fresh water are more effective for obtaining the most
product, rather than a single extraction with a larger volume of water. You can imagine this as
analogous to laundering dirty clothes several times, rather than laundering them with more water—
the cleaner each volume of water is, the less dirt is likely to be left on the clothes afterward.
Once the desired product has been isolated in the solvent, we can obtain the product alone by
evaporating the solvent, usually by using a rotary evaporator (rotovap).
BRIDGE
You can use the properties of acids and bases to your advantage in extraction:HA + base → A– + H–base+When the acid dissociates, the anion formed will be more soluble in the aqueous layer than
the original protonated acid because it is charged. Thus, adding a base will help to extract an
acid into the aqueous phase.Another way to take advantage of solubility properties is to perform the reverse of the extraction we
just described in order to remove unwanted impurities. In this case, a small amount of solute is used
to extract and remove impurities, rather than the compound of interest. This process is called a
wash.
OTHER METHODS
In addition to extraction, filtration and recrystallization make use of solubility characteristics to
separate compounds from a mixture.