Hydroxide

Hydroxide is the polyatomic anion OH⁻, composed of one oxygen atom and one hydrogen atom with a −1 charge. It occurs in bases and many ionic compounds.

Brønsted–Lowry acid–base theory: A theory in which acids donate protons and bases accept them. Hydroxide acts as a proton acceptor, forming water.
Polyatomic ion: A charged species made of two or more covalently bonded atoms. Hydroxide is a two-atom example whose atoms carry a net charge.
Sodium hydroxide: An ionic compound, NaOH, consisting of sodium cations and hydroxide anions. It is a widely used soluble source of hydroxide ions.
pH: A logarithmic measure of hydrogen-ion activity in a solution. In dilute aqueous solutions, hydroxide concentration is related to pH through water’s ion product.
Hydroxyl group: The neutral –OH functional group covalently attached within a molecule. Unlike hydroxide, a hydroxyl group is not by itself a free anion.
Neutralization: A reaction in which an acid and a base reduce each other’s acidic and basic properties. Hydroxide neutralizes acids by accepting their protons.
Ionic bond: An electrostatic attraction between oppositely charged ions. This attraction holds hydroxide in salts such as sodium hydroxide.
Potassium hydroxide: An ionic compound, KOH, consisting of potassium cations and hydroxide anions. It supplies hydroxide in applications including alkaline batteries and soapmaking.
Water autoionization: The proton transfer between water molecules that produces hydronium and hydroxide ions. It establishes the equilibrium that sets hydroxide levels in pure water.
Hydronium: The H₃O⁺ cation formed when a water molecule gains a proton. Hydronium and hydroxide are oppositely charged products of water autoionization.

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