In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na+
and hydroxide anions OH−
.
In chemistry, bases are substances that, in aqueous solution, release hydroxide (OH−) ions, are slippery to the touch, can taste bitter if an alkali, change the color of indicators (e.g., turn red litmus paper blue), react with acids to form salts, promote certain chemical reactions (base catalysis), accept protons from any proton donor or contain completely or partially displaceable OH− ions. Examples of bases are the hydroxides of the alkali metals and the alkaline earth metals (NaOH, Ca(OH)2, etc.—see alkali hydroxide and alkaline earth hydroxide).
In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid and as a base. Many metals (such as copper, zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation states of the oxide. Al2O3 is an example of an amphoteric oxide.
Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric in nature, i.e., it has both basic and acidic properties. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide or alumina (Al2O3), the latter of which is also amphoteric. These compounds together are the major components of the aluminium ore bauxite.
Magnesium hydroxide is the inorganic compound with the chemical formula Mg(OH)2. It occurs in nature as the mineral brucite. It is a white solid with low solubility in water (Ksp = 5.61×10−12). Magnesium hydroxide is a common component of antacids, such as milk of magnesia, as well as laxatives.
A lye is a metal hydroxide traditionally obtained by leaching ashes, or a strong alkali which is highly soluble in water producing caustic basic solutions. "Lye" is commonly an alternative name of sodium hydroxide (NaOH) or historically potassium hydroxide (KOH), though the term "lye" refers to any member of a broad range of metal hydroxides.
Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash.
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is obtained when calcium oxide (called lime or quicklime) is mixed, or slaked with water. It has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater is the common name for a saturated solution of calcium hydroxide.
Lithium hydroxide is an inorganic compound with the formula LiOH. It is a white hygroscopic crystalline material. It is soluble in water and slightly soluble in ethanol, and is available commercially in anhydrous form and as the monohydrate (LiOH.H2O), both of which are strong bases. It is the weakest base among the alkali metal hydroxides.
Zinnwaldite, KLiFeAl(AlSi3)O10(OH,F)2, potassium lithium iron aluminium silicate hydroxide fluoride is a silicate mineral in the mica group. The IMA status is as a series between siderophyllite (KFe2Al(Al2Si2)O10(F,OH)2) and polylithionite (KLi2AlSi4O10(F,OH)2) and not considered a valid mineral species.
Lead(IV) hydroxide, Pb(OH)4, also called ortho-plumbic acid, is the notional conjugate acid of the ortho-plumbate(IV) ion, PbO44−, found in compounds such as calcium orthoplumbate, Ca2PbO4. Like its tin analog Sn(OH)4, Pb(OH)4 has not been isolated.
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide ((C2H5)2SnI2), discovered by Edward Frankland in 1849. The area grew rapidly in the 1900s, especially after the discovery of the Grignard reagents, which are useful for producing Sn-C bonds. The area remains rich with many applications in industry and continuing activity in the research laboratory.
Iron(II) hydroxide or ferrous hydroxide is an inorganic compound with the formula Fe(OH)2. It is produced when iron(II) salts, from a compound such as iron(II) sulfate, are treated with hydroxide ions. Iron(II) hydroxide is a white solid, but even traces of oxygen impart a greenish tinge. The air-oxidized solid is sometimes known as "green rust".
Lead(II) hydroxide, Pb(OH)2, is a hydroxide of lead, with lead in oxidation state +2. It is doubtful that such a simple compound exists. Lead basic carbonate (PbCO3·2Pb(OH)2) or lead(II) oxide (PbO) is encountered in practice where lead hydroxide is expected. This has been a subject of considerable confusion in the past.
Copper(II) hydroxide is the hydroxide of copper with the chemical formula of Cu(OH)2. It is a pale greenish blue or bluish green solid. Some forms of copper(II) hydroxide are sold as "stabilized" copper hydroxide, although they likely consist of a mixture of copper(II) carbonate and hydroxide. Copper hydroxide is a weak base.
Zinc hydroxide Zn(OH)2 is an inorganic chemical compound. It also occurs naturally as 3 rare minerals: wülfingite (orthorhombic), ashoverite and sweetite (both tetragonal).
Metal hydroxides are hydroxides of metals.
