Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Solvent, substance in a solution (a uniform mixture of chemicals) that is in the greatest abundance and typically determines the physical state of the solution. The substance or substances in the solution in smaller amounts are called solutes. Both solvents and solutes can be solids, liquids, or gases. For example, in a solution of salt water, water is the solvent and salt is the solute. In carbonated water, water is the solvent and carbon dioxide gas is the solute. In steel, iron is the solvent and carbon is the solute. Solvents are commercially valuable. They are an important component of paints, lacquers, and pharmaceuticals, and are used in the production of synthetic (artificial) materials.

By selecting the proper solvent, one ingredient or group of ingredients can be separated from a complex substance. This process is called solvent extraction. A solvent can, for example, remove a fragrance or flavor from a complex plant or animal substance. Once dissolved, the fragrance or flavor can be concentrated by then evaporating the solvent. In a well-designed solvent-extraction process, the solvent is recovered and used over and over again. Nearly three-quarters of the soybean oil produced in the U.S. is extracted by the use of liquid hexane as a solvent.

Solvent-extraction systems must be designed and operated with great care. The flavor of a fruit, for example, is not due to a single substance, but to a complex combination of substances. Strawberry essence has more than 80 constituents, and orange flavor has more than 90. If the proportions of these constituents are changed by the solvent extraction process, the aroma or taste may be undesirably altered.

See also Colloid; Essential Oils; Solutions.