General English


  • noun a substance which reacts with an acid to form a salt and water. It may be either a soluble base or a solution of a base that has a pH value of more than 7.


  • A liquid that has a pH greater than 7.0.
  • Water soluble salts of alkali metals, such as sodium and potassium, which occur in concrete and mortar mixes. The presence of alkaline substances may cause expansion and subsequent cracking.


  • A chemical substance that is a base, thus one with a pH value greater than 7.0.
  • A hydroxide formed with one of the alkali metals, such as sodium hydroxide.


  • An alkali is a substance containing a deficiency of hydrogen ions (or an excess of hydroxyl ions) compared with pure water. An alkali (e.g. sodium hydroxide) will combine with an acid (e.g. alginic acid) to form a neutral salt (e.g. sodium alginate). The most common culinary alkalis are sodium bicarbonate and ammonium carbonate both of which liberate carbon dioxide gas when heated or combined with an acid such as tartaric acid.


  • noun one of many substances which neutralise acids and form salts


  • noun a substance that neutralises acids and forms salts

Origin & History of “alkali”

English acquired alkali via Latin from Arabic al-qalīy ‘the ashes’, a derivative of the verb qalay ‘fry’. The implicit reference is to the plant saltwort (Latin name Salsola kali), which was burnt to obtain its alkaline ashes (Chaucer’s canon’s yeoman, the alchemist’s assistant, mentions it: ‘Salt tartre, alcaly, and salt preparat, And combust matieres, and coagulat’, 1386). The modern chemical sense of a compound which combines with an acid to form a salt was first used in 1813, by the chemist Sir Humphry Davy.