What does the term anhydrous refer to?

The term anhydrous specifically refers to a substance that has no water or moisture in its composition. It is often used in the context of chemical compounds that, typically in their hydrated form, contain water molecules as part of their structure, but which have had the water removed, resulting in a dry form.

For example, anhydrous salts, like anhydrous copper(II) sulfate, lack the water molecules that would be present in their hydrated forms. This property is significant in various chemical reactions and processes where the presence of water can alter results or yield different products. Understanding the term anhydrous is essential, as it indicates the complete absence of water, differentiating it from substances that may still contain moisture or are entirely soluble in water.