A chemical compound containing the hydroxyl group.
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A compound containing the hydroxide ion (OH−) and having the general formula M(OH)n, where M represents a metal. Hydroxides are a subset of compounds containing the hydroxyl group (OH) and range in chemical character from strongly basic, to amphoteric (having both acidic and basic characteristics), to essentially acidic. The hydroxide ion has a closed-shell electronic structure with a singlet ground state.
In the Lewis acid-base scheme, where a base is defined as an electron pair donor and an acid as an electron pair acceptor, a typical hydroxide decreases in base strength as attraction for electrons of the cation increases. For example, the hydroxides of electropositive elements such as the alkali metals and alkaline earths tend to be bases. When these ionic compounds are dissolved in water, they form metal ions and hydroxide ions, as in
1 
reaction (1), where S represents a solid and aq represents a water solution. The hydroxides of nonmetals (X) such as boron hydroxide [B(OH)3], where the X-O bonds are covalent, are generally acidic, as shown in reaction (2), where H3O+
2 
is the hydronium ion. The amphoteric hydroxides may dissociate by either mechanism, depending on the presence of strong acids or bases. See also Acid and base; Hydrogen ion.
The alkali metal hydroxides such as sodium hydroxide (NaOH) are extremely important as reagents in metallurgy and photography and in the manufacture of soaps and detergents. Calcium hydroxide [Ca(OH)2], known as slaked lime, is used in the preparation of mortar for brick laying. Minerals such as brucite [Mg(OH)2] and pyrochroite [Mn(OH)2] are naturally occurring hydroxides.
An ionic compound that contains the OH2 ion, usually consisting of metals or the metal equivalent of the ammonium cation (NH42) that inactivates an acid.
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The OH− anion or a compound containing the OH− ion.
| Hydroxide | |
|---|---|
| IUPAC name | hydroxide |
| Systematic name | hydroxide oxidanide hydridooxygenate(1−) |
| Identifiers | |
| CAS number | |
| PubChem | |
| SMILES | [OH-] |
| InChI | InChI=1/H2O/h1H2/ p-1/fHO/h1h/q-1 |
| Properties | |
| Molecular formula | OH− |
| Molar mass | 17.00274 (7) g/mol |
| Acidity (pKa) | ~22 |
| Basicity (pKb) | -1.74 15.74 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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In chemistry, hydroxide is the most common name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known.
Inorganic compounds that contain the hydroxyl group are referred to as hydroxides. Common hydroxides include:
Most compounds containing hydroxide are bases.
An Arrhenius base is a substance that produces hydroxide ions when dissolved in aqueous solution. One example would be ammonia, NH3:
NH3(g) + H2O(l) ⇌ NH4+(aq) + OH−(aq)
Thus, hydroxide ions are heavily involved in acid-base reactions as well as the special double displacement reaction called neutralization.
Salts containing hydroxide are called base salts. Base salts will dissociate into a
cation and one or more hydroxide ions in water, making the solution basic. Base salts will undergo neutralisation reactions with
by omitting spectator ions.
Most inorganic hydroxide salts are insoluble in water, except for those with cations from Group I, NH4+, Ba2+, Sr2+, Ca2+ (little) or Tl+.
Hydroxides and hydroxide ions are relatively common. Many useful chemicals and chemical processes involve hydroxides or hydroxide ions. Sodium hydroxide (lye) is used in industry as a strong base, potassium hydroxide is used in agriculture, and iron hydroxide minerals such as goethite and limonite have been used as low grade brown iron ore. The aluminium ore bauxite is composed largely of aluminium hydroxides.
Hydroxide ion is a kind of ligand. It donates lone pair of electrons, behaving as a Lewis base. Examples of complexes containing such a ligand include the aluminate ion [Al(OH)4]− and aurate ion [Au(OH)4]−.
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| Aluminum Hydroxide |
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