Dichloromethane (DCM), also known as methylene chloride, has a density of approximately 1.37 g/ml. In the context of liquid-liquid extraction involving a water solution, the density of the solvents determines their positioning based on whether they are more or less dense than water.
Water has a density of about 1.00 g/ml at room temperature. Since dichloromethane is denser than water, it will settle at the bottom when the two liquids are mixed. Therefore, in an extraction scenario where dichloromethane is used alongside water, DCM will be the lower layer.
This principle is significant in separations because it allows for the easy collection of one solvent from the bottom layer after extraction is complete. Hence, when using dichloromethane in water, remember that it forms the lower layer due to its higher density.