Definition

Noun: * Hydroxide ion: The anion OH⁻, consisting of one oxygen atom and one hydrogen atom, carrying a negative charge. It is the defining ionic species of a base in the Arrhenius definition.

Usage

• The term "hydroxide ion" is used in chemistry to refer to the negatively charged particle (anion) that is released when a base dissolves in water.
• It is a fundamental concept in acid-base chemistry, often discussed in contrast to the hydrogen ion (H⁺) or hydronium ion (H₃O⁺).

Examples

• Noun:
  • Sodium hydroxide (NaOH) dissociates in water to produce a sodium ion and a hydroxide ion.
  • The concentration of hydroxide ions in a solution determines its pH level.
  • A strong base is a substance that completely ionizes in water to yield hydroxide ions.

Advanced Usage

• "Hydroxide ion concentration": Often denoted as [OH⁻], this is a key parameter for calculating the pOH and pH of a solution.
  • The hydroxide ion concentration was found to be 1 x 10⁻³ M.
• In the context of the autoionization of water, the product of the hydrogen ion and hydroxide ion concentrations is a constant (Kw = [H⁺][OH⁻] = 1 x 10⁻¹⁴ at 25°C).

Variants and Related Words

• Hydroxide (noun): A general term for a compound containing the OH⁻ ion. It can refer to the ionic compound itself (e.g., potassium hydroxide, KOH) or, informally, to the ion.
  • Calcium hydroxide is commonly known as slaked lime.
• Hydroxyl group (noun): The uncharged -OH functional group covalently bonded within a molecule, such as in alcohols (e.g., ethanol, C₂H₅OH). This is distinct from the free hydroxide ion.
  • Methanol contains a hydroxyl group but does not release hydroxide ions into solution.

Synonyms

• OH⁻ ion: The chemical formula is commonly used as a direct synonym.
  • The solution was basic due to a high concentration of OH⁻ ions.

Related Phrases

• Generation of hydroxide ions: Refers to the process by which OH⁻ ions are produced in a reaction.
  • The reaction of an oxide with water can lead to the generation of hydroxide ions.

Noun

1. the anion OH having one oxygen and one hydrogen atom