The water of crystallization is commonly known by its scientific name, water of crystallization, or sometimes referred to as water of hydration. While there isn't a simpler, single-word common name distinct from its scientific term for the water itself, the compounds containing it are widely known as hydrates or hydrated salts.
This term refers to the water molecules that are chemically bonded within the crystal structure of certain salts and compounds. These water molecules are integral to the crystal's structure and properties.
Understanding Water of Crystallization
Water of crystallization is crucial to the crystalline form and stability of many inorganic salts. It is distinct from interstitial water, which is simply trapped within the crystal lattice, or surface water, which is adsorbed onto the crystal surface.
- Definition: Water of crystallization is the water associated with the crystal (or molecule) of any salt.
- Role: It contributes to the crystal's shape, color, and other physical characteristics.
- Removal: This water can typically be removed by heating, which often causes the crystal structure to break down, resulting in an anhydrous (water-free) form and sometimes a change in color or appearance.
Common Names of Hydrated Compounds
While the water itself retains its scientific descriptor, the compounds that incorporate it often have common names. These compounds are generally referred to as hydrated salts or simply hydrates.
A well-known example highlighted in chemistry is washing soda.
- Washing Soda: This common household product is actually sodium carbonate decahydrate (Na₂CO₃·10H₂O). It is a hydrated salt containing ten molecules of water of crystallization per molecule of sodium carbonate.
| Common Name | Chemical Name | Molecular Formula | Number of Water Molecules |
|---|---|---|---|
| Washing Soda | Sodium Carbonate Decahydrate | Na₂CO₃·10H₂O | 10 |
| Gypsum | Calcium Sulfate Dihydrate | CaSO₄·2H₂O | 2 |
| Epsom Salt | Magnesium Sulfate Heptahydrate | MgSO₄·7H₂O | 7 |
| Blue Vitriol | Copper(II) Sulfate Pentahydrate | CuSO₄·5H₂O | 5 |
Importance and Applications
The presence of water of crystallization is not merely an incidental feature; it significantly influences the properties and applications of these compounds:
- Color Changes: Many salts change color when their water of crystallization is removed. For example, hydrated copper(II) sulfate is blue, while its anhydrous form is white.
- Structural Stability: The water molecules help to stabilize the crystal lattice, influencing its shape and hardness.
- Industrial Uses:
- Washing Soda (Sodium Carbonate Decahydrate): Used in detergents, as a water softener, and in glass manufacturing. Its water content makes it less prone to caking than anhydrous sodium carbonate.
- Gypsum (Calcium Sulfate Dihydrate): Essential for plaster of Paris, drywall, and agricultural soil amendment.
- Epsom Salt (Magnesium Sulfate Heptahydrate): Used in bath salts for therapeutic purposes and as a laxative.
The term "water of crystallization" thus functions as both its scientific and most common descriptive name, while specific hydrated compounds may have their own familiar common names.
