hydroxidjonen

Hydroxidjonen, or the hydroxide ion, is the negatively charged polyatomic anion with the formula OH−. It consists of one oxygen atom bonded to one hydrogen atom, carrying an overall −1 electric charge. In aqueous solutions the hydroxidjonen acts as a Brønsted–Lowry base, ready to accept protons and form water.

Formation and occurrence

The hydroxidjonen forms whenever bases dissolve in water or when water autoionizes and reactions shift the balance toward basic conditions. In pure water, the equilibrium 2 H2O ⇌ H3O+ + OH− sets a low but nonzero concentration of OH−. Strong bases, such as sodium hydroxide, dissociate in water to yield Na+ and OH−. The concentration of hydroxidjonen in solution is a key determinant of pH; higher OH− concentrations correspond to more basic, alkaline solutions.

Properties and reactivity

As a base, the hydroxidjonen readily neutralizes acids to produce water and a corresponding salt: OH− + H3O+ → 2 H2O. It is a strong nucleophile in many chemical reactions and participates in precipitation reactions with metal ions to form metal hydroxides (for example, Fe3+ reacts with OH− to form Fe(OH)3). The solubility of metal hydroxides varies: alkali metal hydroxides (like NaOH, KOH) are highly soluble, while many alkaline earth hydroxides (such as Ca(OH)2) are only sparingly soluble.

Applications and safety

Hydroxidjonen is central to many industrial processes, including the production of caustic soda (sodium hydroxide) via electrolysis, pH adjustment in water treatment, and various chemical syntheses. It also plays a role in soil chemistry and environmental boundaries between acidic and basic conditions. The compound is caustic and can cause severe burns; proper handling and protective measures are essential.

In summary, hydroxidjonen is a fundamental base in aqueous chemistry, governing many reactions and processes through its basic, water-forming behavior.