Hydroxide Ions
Acid and Bases are defined according to three different theories and concepts.
A) Arrhenius Concept
B) Lowry Bronsted Theory
C) Lewis Theory
According to Arrhenius Concept of Acid and Base, "Acid is any specie which when dissolved in water ionizes to produce H⁺ ions".
Examples:
HNO₃ → H⁺ + NO₃⁻
H₃PO₄ → 3 H⁺ + PO₄³⁻
While, "Bases are those species which when dissolved in water produces Hydroxyl Ions (OH⁻)".
Examples:
KOH → K⁺ + OH⁻
Ca(OH)₂ → Ca²⁺ + 2 OH⁻