Anhydrous

Anhydrous describes a substance that is free from water. The term is most often used in chemistry to refer to chemical compounds or materials that contain no water molecules, either chemically bound (as in a hydrate) or physically adsorbed. The process of removing water from a substance to make it anhydrous is called dehydration.

The degree to which a substance is considered anhydrous can vary. For example, a compound might be described as "anhydrous" even if it contains trace amounts of water, provided that the water content is below a specified tolerance level. Special handling and storage techniques, such as using desiccators or dry boxes, are often necessary to maintain the anhydrous state of highly reactive compounds.

Anhydrous forms of chemicals often have different properties compared to their hydrated counterparts, including differences in solubility, melting point, reactivity, and stability. This difference in properties makes anhydrous chemicals crucial in various applications, including organic synthesis, pharmaceutical manufacturing, and materials science.

The preparation of anhydrous compounds typically involves heating, vacuum drying, or the use of chemical drying agents (desiccants) that react with or absorb water. Common desiccants include anhydrous magnesium sulfate, anhydrous calcium chloride, and molecular sieves.