hydrate

A solid compound containing water molecules combined in a definite ratio as an integral part of the crystal.

1. To rehydrate.
2. To supply water to (a person, for example) in order to restore or maintain fluid balance: “Cold water is the fastest and safest way to hydrate an ordinary athlete” (Jane E. Brody).

To become a hydrate.

A particular form of a solid compound which has water in the form of H₂O molecules associated with it. For example, anhydrous copper sulfate is a white solid with the formula CuSO₄. When crystallized from water, a blue crystalline solid which contains water molecules as part of the crystals is formed. Analysis shows that the water is present in a definite amount, and the hydrate may be given the formula CuSO₄ · 5H₂O. Four of the water molecules are attached to the copper ion in the manner of coordination complexes, and the fifth water molecule is related to the sulfate and presumably held by hydrogen bonding. See also Hydrogen bond.

Water can also be present in definite proportions in the crystal without being associated directly with the anion or cation. The water occupies a definite place in the crystal lattice. Alums, with their 12 molecules of water, are examples of this. See also Alum.

Gas hydrates (gas clathrates) are crystalline compounds in which an isometric (cubic) ice (H₂O) lattice contains cages that incorporate small guest gas molecules. They are stable at moderate to high pressures and low temperatures, above and below the ice point. These ice lattices are stable only when the cages contain a gas molecule. The pressure and temperature constraints restrict them to oceanic continental margins in the uppermost few hundred meters of slope and rise sediments where water depths exceed 300–500 m (1000–1600 ft), and to permafrost in polar regions. Under the ocean, the amount of gas hydrates is at least an order of magnitude higher than in permafrost.

Methane (CH₄) hydrate is the dominant natural gas hydrate on Earth. One cubic meter of methane hydrate when dissociated can contain 165–180 m³ of methane gas. The total amount of methane in gas hydrates is estimated to be very large; about 10¹⁹ g of methane carbon is stored in them, approximately twice that in fossil fuels.

Recent interest in natural gas hydrates, most of which are methane hydrates, has resulted from the recognition that global warming may destabilize the enormous quantities of methane hydrate in shallow marine slope sediments and permafrost. The environmental impact of releasing large quantities of methane into the ocean and atmosphere could have important consequences. The fossil fuel resource potential of the enormous quantities of marine methane hydrates is being evaluated. See also Methane.

1. To combine with water or elements of water.
2. Hydrated lime.

1. a compound of water with a radical.
2. a salt or other compound that contains water of crystallization.

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.

Contents 1 Chemical nature of hydrates 1.1 Organic chemistry 1.2 Inorganic chemistry 2 Applications of hydrates 2.1 Construction 2.2 Passive fire protection (PFP) 3 See also 4 References

Chemical nature of hydrates

Organic chemistry

In organic chemistry, a hydrate is a compound formed by the addition of water or its elements to another molecule. For example, ethanol, CH₃—CH₂—OH, can be considered as a hydrate of ethylene, CH₂=CH₂, formed by the addition of H to one C and OH to the other C. A molecule of water may be eliminated, for example by the action of sulfuric acid. Another example is chloral hydrate, CCl₃—CH(OH)₂, which can be formed by reaction of water with chloral, CCl₃—CH=O.

Molecules have been labeled as hydrates for historical reasons. Glucose, C₆H₁₂O₆, was originally thought of as C₆(H₂O)₆ and described as a carbohydrate, but this is a very poor description of its structure as known today. And methanol is often sold as “methyl hydrate”, implying an incorrect formula CH₃OH₂, although the correct formula is CH₃—OH.

Inorganic chemistry

Hydrates are inorganic salts "containing water molecules combined in a definite ratio as an integral part of the crystal"^[1] that are either bound to a metal center or that have crystallized with the metal complex. Such hydrates are also said to contain water of crystallization or water of hydration. If the water is heavy water, where the hydrogen involved is the isotope deuterium, then the term deuterate may be used in place of hydrate.

Anhydrous Cobalt(II) chloride CoCl₂

Cobalt(II) chloride hexahydrate Co(H₂O)₆Cl₂

A colorful example is cobalt(II) chloride, which turns from blue to magenta (red) upon hydration, and can therefore be used as a water indicator.

The notation of hydrous compound · nH₂O, where n is the number of water molecules per molecule of salt, is commonly used to show that a salt is hydrated. The n is usually a low integer, though it is possible for fractional values to exist. In a monohydrate n is one, in a hexahydrate n is 6 etc. Such water is also referred to as water of crystallization. Examples include borax decahydrate and chalcanthite.

Gas hydrates are clathrate hydrates (a class of solid hydrates of gases): water ice with gas molecules trapped within. When the gas is methane it is called a methane hydrate.

A hydrate which has lost water is referred to as an anhydride, and can normally lose further water only upon strong heating, if at all. A substance that does not contain any water is referred to as anhydrous.

Applications of hydrates

Construction

Generally, in construction and refractories, inorganic binders are often deprived of water during manufacture. For instance, both in cement and gypsum products, heat is applied to the raw materials. Once water is added on a construction site, the powder is re-hydrated and able to form bonds with other substances that are present. Thus, one goes from powder, to slurry, or paste and then forms "cement stone". Water that is not chemically bound, or converted into hydrates, can come off again as steam, especially due to the heat of hydration, with cement products in particular, which undergo an exothermic chemical reaction with water.

Generally, the longer one can keep cementitious products wet immediately after placement, the better. The wetter cementitious products are kept, the more water will be converted into hydrates, instead of evaporating off due to the heat of hydration and other environmental influences. Premature drying is a cause for severe concrete problems, such as cracking and shrinking.

Passive fire protection (PFP)

Avoiding premature drying is important to all other cementitious building products, particularly spray fireproofing and firestop mortars, where the slightest cracking can lead to rejection. The chemically bound water is used up by endothermic reactions when exposed to the heat of a fire. Fire temperatures in a building can reach 1100°C, depending on the fuel present and the availability of oxygen, but the hydrates keep the temperature of the item near 100 °C until all the water is spent. Therefore, the more hydrates, the longer the fire-resistance duration. This is what lends fire-resistive characteristics to basic, or "old" building materials, like gypsum, concrete or plaster.

Fire-resistance duration is important to many high-tech PFP products such as intumescent and endothermic paints, wraps and tiles, such as those used in space physics for re-entry vehicles.

See also

• Passive fire protection
• Water of crystallization

References

1. ^ "Hydrate". Farlex, Inc (TheFreeDictionary.com. http://www.thefreedictionary.com/hydrate. Retrieved on 2009-07-08. 

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - hydrat, hydrering
v. tr. - hydrere, tilsætte vand til
v. intr. - hydrere

Nederlands (Dutch)
hydraat (scheikunde), water toevoegen, overgaan in een hydraat

Français (French)
n. - hydrate
v. tr. - hydrater
v. intr. - hydrater

Deutsch (German)
n. - (Chem.) Hydrat
v. - chemisch mit Wasser verbinden

Ελληνική (Greek)
n. - (χημ.) ένυδρο άλας
v. - (χημ.) ενυδατώνω/-ομαι

Italiano (Italian)
idrato, idratare

Português (Portuguese)
n. - hidrato (m) (Quím.)
v. - hidratar

Русский (Russian)
гидрат, гидратировать

Español (Spanish)
n. - hidrato
v. tr. - hidratar
v. intr. - hidratar

Svenska (Swedish)
n. - hydrat
v. - hydratisera

中文（简体）(Chinese (Simplified))
水合物, 氢氧化物, 使成水化合物, 水合

中文（繁體）(Chinese (Traditional))
n. - 水合物, 氫氧化物
v. tr. - 使成水化合物
v. intr. - 水合

한국어 (Korean)
n. - 함수화합물, 수화물
v. tr. - 수화시키다, 수산화시키다
v. intr. - 수화하다, 수산화하다

日本語 (Japanese)
n. - 水和物, 含水化合物
v. - 水和する

العربيه (Arabic)
‏(الاسم) هيدرات, ايدرات, ماءات (فعل) يميه يجعله يتحد مع الماء, يتميه يتحد مع الماء‏

עברית (Hebrew)
n. - ‮תרכובת המכילה מים, מימה‬
v. tr. - ‮הרכיב כימית עם מים‬
v. intr. - ‮הורכב כימית עם מים‬

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