Heptahydrate

Heptahydrate refers to a chemical compound that has incorporated seven molecules of water into its crystal structure. This form of hydration is known as a hydrate. When a substance forms a heptahydrate, it means that for every molecule of the anhydrous (water-free) compound, there are seven water molecules associated with it. The water molecules are often referred to as water of crystallization or water of hydration.

The presence of these water molecules can significantly alter the physical properties of the compound, such as its solubility, melting point, and appearance. For example, a heptahydrate might be crystalline and stable under certain conditions, but upon heating, it can lose its water molecules to become an anhydrous form or a hydrate with a different water content. The specific number of water molecules in a hydrate is often indicated by a prefix. "Hepta-" signifies seven.

A common example of a heptahydrate is sodium sulfate heptahydrate, also known as Glauber's salt, with the chemical formula Na₂SO₄·7H₂O. Another well-known example is magnesium sulfate heptahydrate, commonly called Epsom salt, with the formula MgSO₄·7H₂O. The formation and stability of heptahydrates are dependent on factors like temperature and humidity.