Definition of alkali in US English:

nounPlural alkalis

• A chemical compound that neutralizes or effervesces with acids and turns litmus blue; typically, a caustic or corrosive substance of this kind such as lime or soda.

  Alkalis release hydroxide ions (OH⁻) when dissolved in water. Any solution with a pH of more than 7 is alkaline

  ‘flint is not subject to chemical weathering except by strong alkalis’

  Often contrasted with acid; compare with base

  mass noun ‘the reaction is followed by measuring the concentration of alkali at various times’

  More example sentences

  • ‘Caustic alkalis react with the paint coating and loosen it from the surface.’
  • ‘Tellurium reacts with both acids and some alkalis.’
  • ‘Like semi-permanent dyes, permanent dyes are also alkalis.’
  • ‘Platinum also dissolves in hot alkalis such as hot sodium hydroxide or potassium hydroxide.’
  • ‘Nitriles can be decomposed by acids or alkalis to give the corresponding carboxylic acid or they can be reduced to give primary amines.’
  • ‘Zinc is a fairly active metal that dissolves in both acids and strong alkalis.’
  • ‘Carboxylic acids also react with alkalis, or bases.’
  • ‘It combines with most non-metals at high temperatures and reacts with both acids and alkalis.’
  • ‘The high-density overlay protects the wood substrate from alkalis and water.’
  • ‘They resist most chemicals, including many acids, alkalis, oxidizing agents, and solvents.’
  • ‘Nickel has good resistance to corrosion in the normal atmosphere, in natural freshwaters and in deaerated nonoxidizing acids, and it has excellent resistance to corrosion by caustic alkalis…’
  • ‘Concentrated acids and caustic alkalis should be handled with the greatest care.’
  • ‘Chemically, aluminum will react with the alkalis in concrete and produce hydrogen bubbles.’
  • ‘Amides are hydrolysed to ammonium salts with catalysis by acids or alkalis.’
  • ‘Corrosives (mineral acids, alkalis, phenols) are in this category.’
  • ‘It can withstand high temperatures and is resistant to many corrosive substances such as acids and alkalis.’
  • ‘It accounted for acids and alkalis, for respiration and the smells of plants.’
  • ‘On contact, strong acids, alkalis, and heavy metals cause chemical burns.’
  • ‘Soap is made by combining a fat source (either animal or vegetable) and an alkali in a chemical process known as saponification.’
  • ‘Copper is a moderately reactive metal that dissolves in most acids and alkalis.’

  Synonyms

  caustic, corroding, eroding, erosive, abrasive, biting, mordant, burning, stinging

  View synonyms