hydrate (redirected from Pentahydrate)

hydrate (hī`drāt), chemical compound that contains water. A common hydrate is the familiar blue vitriol, a crystalline form of cupric sulfate. Chemically, it is cupric sulfate pentahydrate, CuSO₄·5H₂O. When a crystal of the substance is formed, five molecules of water (H₂O) are combined in the crystal with each molecule of cupric sulfate (CuSO₄). This water is called water of crystallization. When cupric sulfate pentahydrate is heated above 150°C; the water of crystallization is driven off and anhydrous cupric sulfate is formed. It has several properties different from the pentahydrate, e.g., color, density, and crystal structure. Glauber's salt is sodium sulfate decahydrate, Na₂SO₄·10H₂O. Crystals of it readily give up their water of crystallization at ordinary temperatures, forming a powdery coating of the anhydrous salt; this phenomenon (efflorescence) is exhibited by many hydrates. The number of molecules of water present in a given hydrate is fixed. However, some substances form several different hydrates. There are four different hydrates of ferrous sulfate, each with its own unique physical properties. In organic chemistry a compound formed by addition of water to a carbon-carbon double bond is sometimes called a hydrate; it contains a hydroxyl functional group and usually cannot be dehydrated. In commerce a metal hydroxide is sometimes called a hydrate; e.g., calcium hydrate is calcium hydroxide.

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hydrate

1. a chemical compound containing water that is chemically combined with a substance and can usually be expelled without changing the constitution of the substance

2. a chemical compound that can dissociate reversibly into water and another compound. For example sulphuric acid (H₂SO₄) dissociates into sulphur trioxide (SO₃) and water (H₂O)

3. a chemical compound, such as a carbohydrate, that contains hydrogen and oxygen atoms in the ratio two to one

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hydrate [′hī‚drāt]

(chemistry)

A 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, but when crystallized from water a blue crystalline solid with formula CuSO₄·5H₂O results, and the water molecules are an integral part of the crystal.

A crystalline compound resulting from the combination of water and a gas; frequently a constituent of natural gas that is under pressure.

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hydrate

1. To combine with water or elements of water.

2. Hydrated lime.