temporarily mixed by shaking so that solute can pass from one solvent to the other. For example, in
a solution of isobutyric acid and diethyl ether, shown in Figure 12.1, we can extract the isobutyric
acid with water. Isobutyric acid, with its polar carboxyl group, is more soluble in a polar solvent like
water than in a nonpolar solvent like ether. When the two solvents are mixed together, isobutyric
acid will transfer to the water layer, which is called the aqueous phase (layer). The nonpolar ether
layer is called the organic phase (layer).
Figure 12.1. Isobutyric Acid and Diethyl Ether
Isobutyric acid is more polar than diethyl ether and can exhibit hydrogen bonding, so it will
congregate in the aqueous layer; diethyl ether will remain in the organic layer.MCAT EXPERTISE
Think of the organic and aqueous layers as being like the oil and water in salad dressings:
you can shake the mixture to increase their interaction, but ultimately they will separate
again.After the two layers are mixed together, how do we then get the desired product out? The water
(aqueous) and ether (organic) phases will separate on their own, given time to do so. In order to
isolate these two phases, we use a piece of equipment called a separatory funnel, as shown in
Figure 12.2. Gravitational forces cause the denser layer to sink to the bottom of the funnel, where it
can then be removed by turning the stopcock at the bottom. It is more common for the organic
layer to be on top, although the opposite can also occur. Remember that the position of the layers is
determined by their relative densities.