An acid can be defined as a compound that, when dissolved in water, gives hydronium ions (H3O+).
An alkali (or a base) is a compound that yields hydroxyl ions (OH–) as the only negatively charged ion when dissolved in water.
Arrhenius acids and bases
The Arrhenius theory of acids and bases was originally proposed by the Swedish chemist Svante Arrhenius in 1884. An Arrhenius acid is any species that increases the concentration of H+ ions or protons in an aqueous solution. An Arrhenius base is defined as any species that increases the concentration of hydroxide ions OH- ions.
- Arrhenius acid increases the concentration of H+ ions.
- An Arrhenius base increases the concentration of OH- ions.
- In an acid-base or neutralization reaction, an Arrhenius acid and base usually react to form water and salt.