Structure and Properties
The ones with small carbon chains such as sodium acetate are crystalline ionic network materials. You may recall working with crystals of sodium acetate last term in the supersaturation experiment.
However, if the carbon chain is very long, it gets in the way and an orderly network of ions is not possible. The material is still solid but not crystalline. Soap is an example of a long chained carboxylate salt. Soaps are generally the sodium or potassium salts of fatty acids.
Solubilty in Water
Two factors determine the solubility of carboxylate salts in water.
One is the nature of the carboxylate ion -- its length, shape, amount of branching and so on. The larger and less polar this group is, the less soluble it is in water. Our traditional five-carbon-atom cutoff point for solubility in water is not appropriate for carboxylate ions. The reason is that the carboxylate functional group is not merely polar, it is ionic. This allows for stronger ion-dipole bonds to be formed with the water molecules and pull longer carbon chains into solutions. Soaps, for example, generally have from twelve to eighteen carbon atoms in the carbon chain.
E-mail instructor: Sue Eggling
Clackamas Community College