hydrate

hydrate
hydration, n.
/huy"drayt/, n., v., hydrated, hydrating.
n.
1. any of a class of compounds containing chemically combined water. In the case of some hydrates, as washing soda, Na2CO3·10H2O, the water is loosely held and is easily lost on heating; in others, as sulfuric acid, SO3·H2O, or H2SO4, it is strongly held as water of constitution.
v.t., v.i.
2. to combine chemically with water.
[1795-1805; HYDR-1 + -ATE2]

* * *

 any compound containing water in the form of H2O molecules (molecule), usually, but not always, with a definite content of water by weight. The best-known hydrates are crystalline solids that lose their fundamental structures upon removal of the bound water. Exceptions to this are the zeolites (zeolite) (aluminum silicate minerals (silicate mineral) or their synthetic analogues that contain water in indefinite amounts) as well as similar clay minerals (clay mineral), certain clays, and metallic oxides (oxide), which have variable proportions of water in their hydrated forms; zeolites lose and regain water reversibly with little or no change in structure.

      Substances that spontaneously absorb water from the air to form hydrates are known as hygroscopic or deliquescent, whereas hydrates that lose so-called water of hydration or water of crystallization to form the unhydrated (anhydrous) substances are known as efflorescent. In many cases, the uptake and loss of water (by heating, decreasing pressure, or other means) are reversible processes, sometimes accompanied by changes in colour. For example, blue vitriol, or copper sulfate pentahydrate (CuSO4∙5H2O), is blue, copper sulfate trihydrate (CuSO4∙3H2O) is blue, and anhydrous copper sulfate (CuSO4) is white.

      Other examples of hydrates are Glauber's salt (sodium sulfate decahydrate, Na2SO4∙10H2O); washing soda (sodium carbonate decahydrate, Na2CO3∙10H2O); borax (sodium tetraborate decahydrate, Na2B4O7∙10H2O); the sulfates known as vitriols (vitriol) (e.g., Epsom salt, MgSO4∙7H2O); and the double salts known collectively as alums (M+2SO4∙M+32(SO4)3∙24H2O, where M+ is a monopositive cation, such as K+or NH4+, and M3+ is a tripositive cation, such as Al3+ or Cr3+).

      In many cases, hydrates are coordination compounds (coordination compound). CuSO4∙5H2O is actually [Cu(H2O) 4]SO4∙4H2O; four molecules of water of hydration are coordinated to the copper ion, whereas the fifth water molecule is linked to the sulfate ion, presumably by hydrogen bonding. Similarly, MgSO4∙7H2O is actually [Mg(H2O) 6]SO4∙4H2O. X-ray diffraction studies have shown that hydrated beryllium sulfate (BeSO4∙4H2O) and hydrated beryllium nitrate (Be(NO3)2∙4H2O) both contain the tetrahedral complex ion [Be(H2O) 4]4+.

      A number of gases—notably the noble gases (noble gas) and simple hydrocarbon gases such as methane, ethane, propane, and acetylene, as well as chlorine and carbon dioxide—form crystalline hydrates called clathrate compounds at relatively low temperatures and pressures. Clathrate crystals have a structure in which the water molecules form a loosely held framework surrounding the gas molecule.

George B. Kauffman

Additional Reading
The chemistry of hydrates is covered in Mary Martinette Hagan, Clathrate Inclusion Compounds (1962); Jon A. McCleverty and Thomas Meyer (eds.), Comprehensive Coordination Chemistry II: From Biology to Nanotechnology, 10 vol. (2003); and Robyn V. Young and Suzanne Sessine (eds.), World of Chemistry (2000).

* * *


Universalium. 2010.

Игры ⚽ Поможем сделать НИР
Synonyms:

Look at other dictionaries:

  • hydrate — [ idrat ] n. m. • 1802; du gr. hudôr « eau » ♦ Chim. 1 ♦ Composé renfermant une ou plusieurs molécules d eau. Le plâtre de Paris (Ca2SO4H2O) est un hydrate. 2 ♦ Vieilli Hydrate de carbone : glucide. Régime sans hydrates de carbone. ● hydrate nom… …   Encyclopédie Universelle

  • Hydrate — is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood …   Wikipedia

  • Hydrate — Hy drate, n. [Gr. y dwr water: cf. F. hydrate.] (Chem.) (a) A compound formed by the union of water with some other substance, generally forming a neutral body, as certain crystallized salts. (b) A substance which does not contain water as such,… …   The Collaborative International Dictionary of English

  • hydrate — (n.) 1802, compound of water and another chemical, from Fr. hydrate, coined c.1800 by French chemist Joseph Louis Proust (1754 1826) from Gk. hydr , stem of hydor water (see WATER (Cf. water) (n.1)). The verb is first attested 1850, to form a… …   Etymology dictionary

  • hydrate — [hī′drāt΄] n. [ HYDR(O) + ATE1] a compound formed by the chemical combination of water and some other substance in a definite molecular ratio [plaster of Paris, 2CaSO4·H2O, is a hydrate] vt., vi. hydrated, hydrating 1. to become or cause to… …   English World dictionary

  • Hydrate — Hy drate, v. t. [imp. & p. p. {Hydrated}; p. pr. & vb. n. {Hydrating}.] To form into a hydrate; to combine with water. [1913 Webster] …   The Collaborative International Dictionary of English

  • Hydrate — (Hydroxyde), Verbindungen von Oxydulen und Oxyden mit Wasser. Man kann sie auffassen als Substitute der Oxyde, in denen die Sauerstoffatome durch Hydroxyl vertreten sind. Je nachdem sich die Hydrate von Oxyden oder Oxydulen ableiten, werden sie… …   Lexikon der gesamten Technik

  • hydraté — hydraté, ée (i dra té, tée) part. passé d hydrater. Qui contient de l eau à l état de combinaison.    Acide hydraté, se dit souvent d un acide contenant de l eau qui n est pas combinée …   Dictionnaire de la Langue Française d'Émile Littré

  • Hydrate — Hydrate, chemische Verbindungen des Wassers mit Metalloxyden, Säuren etc. Das Wasser, Hydratwasser, nimmt bei ersteren die Stelle der Säure, bei letzteren die Stelle der Base ein, u. wird verdrängt, wenn sich beide zu einem Salz verbinden …   Pierer's Universal-Lexikon

  • Hydrāte — Hydrāte, nach den ältern Anschauungen in der Chemie Verbindungen von Oxyden oder wasserfreien Säuren mit Wasser. Kaliumoxyd bildet demnach mit Wasser das Kaliumoxydhydrat K2O.H2O (das heutige Kaliumhydroxyd KHO). Schwefelsäure SO3.H2O ist nach… …   Meyers Großes Konversations-Lexikon

  • Hydrate — Hydrate,   Singular Hydrat das, (e)s, durch Hydratation gebildete Verbindungen von Wasser mit anderen Molekülen oder Ionen. In festen Hydraten sind die Wassermoleküle entweder koordinativ an die Ionen gebunden (z. B. beim Hexaaquaaluminiumion… …   Universal-Lexikon

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”