Density

Another consideration when selecting an extraction solvent is its density. Solvents that are more dense than water will form the lower layer of the pair when mixed together, while solvents that are less dense than water will form the upper layer or ‘‘float’’ on water.

  For example, ethyl ether has a density of 0.7133 g/mL at 20º C and would constitute the upper phase when combined with water, which has a density of 0.9982 g/mL at that temperature. On the other hand, the density of chloroform is 1.4892 at 20º C. Therefore, water would form the top layer in a water–chloroform solvent pair.