crystal water is the name for water, which occurs in the crystalline solid body bound. Crystal-aqueous substances are called often also hydrates. Thus there is z. B. crystal water-free sodium sulfate well 2 SO 4 and the Dekahydrat (Glauber's salt) with 10 (lat.: deka= ten) Water molecules per formula unit well 2 SO 4. The connection is symbolized by a highranking point (sometimes also an x), this way of writing gives however no information over the kind of the connection: Well 2 SO 4 · 10 H 2 O.
The water molecules can coordinatively bound at ions its (co-ordination water, z. B. with copper sulfate), when structure water over hydrogen bonds bound to molecules are present, or - as with zeolites - not involved in the crystal lattice its. Connection conditions of the water are most varied in protein crystals.
The crystal water is usually onlyloosely bind and escapes with heating (technical expression up:Calcinieren, burning), which can lead with copper sulfate to the decolorization, with other substances even to the dissolution in the own crystal water.
The crystal water-free salts are called Anhydrate. (z. B. Sodium sulfate Anhydrat, copper sulfate Anhydrat, not to confound with anhydrite and anhydride). Anhydrate are usually strongly hygroscopic substances and therefore for drying solvents and gases are used.
With the formation of hydrates then energy becomes free in the form of heat of hydration.
demarcation of Gashydraten
of Gashydrate (like methane ice), are actually no hydrates, butInclusion connections (Klathrate). Here the gases are stored in the structure cavities of crystalline water, one speak thereby not of crystal water since the water molecules themselves produce the structure. The enclosed atoms or molecules are as also in a cage in the structure imprisoned, therefore thatName cage connections. When melting the water the gases are then again set free.
utilization in the technology
technical one uses the fortune of the gypsum to take up that by heating up (burn) partly or completely lost crystal waters when touching with water again and therebyto confirm. With heating the dihydrate CaSO up 4·2H 2 O on approximately 110 °C develops burned gypsum (hemihydrate and/or. Hemihydrat mentioned, CaSO 4·1/2H 2 O), with 130 to 160 °C Stuckgips (mixture from much hemihydrate and little anhydrite).
Anhydrite comes also as Mineral in salt deposit places forwards and consists of crystal water-free calcium sulfate (CaSO 4). A further technical application is shifting the desiccator silicagel with cobalt chloride, which is colored in the crystal water-free condition blue and in the crystal-aqueous pink, the silicagel must then by heating up be regenerated.