heptahydraatti

Heptahydraatti refers to a crystalline solid that contains seven molecules of water per molecule of the anhydrous compound. This water is incorporated into the crystal lattice structure and is known as water of hydration. The presence of these water molecules significantly influences the physical properties of the compound, such as its melting point, solubility, and density, compared to its anhydrous form.

Many common salts can exist as heptahydrates. A well-known example is sodium sulfate decahydrate, often called Glauber's salt, which is a decahydrate (ten water molecules). However, heptahydrates are also prevalent. For instance, magnesium sulfate heptahydrate, commonly known as Epsom salt, is a familiar example. Another common example is iron(II) sulfate heptahydrate.

The number of water molecules in a hydrate is indicated by a prefix. "Hepta-" signifies seven. Other common hydrates include monohydrates (one water molecule), dihydrates (two), trihydrates (three), tetrahydrates (four), pentahydrates (five), hexahydrates (six), and decahydrates (ten). The specific hydrate form a compound takes can depend on the conditions under which it crystallizes, such as temperature and humidity. When a heptahydrate is heated, it can lose its water of hydration, transforming into a lower hydrate or the anhydrous form. This process is called dehydration. Conversely, anhydrous salts can absorb moisture from the air to form hydrates, a process known as hydration or efflorescence if the water is then lost again.