Hydraattiryhmä

Hydraattiryhmä, meaning "hydrate group" in Finnish, refers to a collection of chemical compounds that contain water molecules incorporated into their crystal structure. These water molecules, known as water of crystallization or hydration water, are not chemically bonded to the main compound but are held within the crystal lattice by weaker forces such as hydrogen bonds or electrostatic interactions. The presence and number of these water molecules can significantly influence the physical properties of the compound, including its melting point, solubility, and density.

The formation of hydrates is common in many inorganic salts, such as copper sulfate pentahydrate (CuSO4·5H2O), where five water molecules are associated with each copper sulfate unit. Other examples include gypsum (calcium sulfate dihydrate, CaSO4·2H2O) and washing soda (sodium carbonate decahydrate, Na2CO3·10H2O). The hydration can be a reversible process; heating a hydrate can often drive off the water molecules, forming an anhydrous (water-free) compound. Conversely, anhydrous compounds can reabsorb water from the atmosphere to form hydrates under suitable conditions, a process known as efflorescence or deliquescence depending on the compound's properties. Understanding the hydration state is crucial in various applications, including chemistry, material science, and pharmacy, as it impacts the stability, reactivity, and handling of these substances.