Hydroxide

Hydroxide refers to the hydroxide ion, OH−, a negatively charged polyatomic ion consisting of one oxygen atom bonded to one hydrogen atom. The term also appears in references to hydroxide-containing compounds, such as metal hydroxides like sodium hydroxide (NaOH), and, in organic chemistry, to the hydroxyl functional group (-OH) that is part of many molecules; that group is more commonly called a hydroxyl group.

In water, hydroxide ions are responsible for basic solutions. They are produced when acids react with bases, when alkali metal hydroxides dissolve in water, or by the electrolysis of water and brine. Industrially, sodium hydroxide is produced by electrolysis of concentrated brine; calcium hydroxide is prepared by slaking quicklime (calcium oxide) with water; other metal hydroxides form by reaction of metals or metal oxides with water or acids.

Solubility varies: alkali metal hydroxides such as NaOH and KOH are highly soluble, while many other metal hydroxides are sparingly soluble. Hydroxides react with acids in neutralization reactions to form water and a salt. They also react with carbon dioxide to form carbonates or bicarbonates in aqueous solution. As bases, hydroxide ions donate electron pairs (Bronsted-Lowry) or act as Lewis bases.

Applications include chemical manufacture, papermaking, and soap production; use in water treatment to raise pH and neutralize acidity; construction uses calcium hydroxide in cement chemistry; and household products rely on NaOH or KOH as strong bases and cleaners.

Safety: hydroxide sources are caustic and can cause severe skin and eye burns; handle with appropriate PPE and store away from acids and reactive materials.