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Hydroxide lewis structure.pngHydroxide 3d model.png

Systematic name Hydroxide
Other names Hydroxyl
Molecular formula OH−
Molar mass Molar mass::17.01 g/mol
Appearance Solid[1]
CAS number CAS number::14280-30-9
Acidity (pKa) 15.7[2]
Basicity (pKb) -1.8[2]
Chiral rotation [α]D 90°

Hydroxide is a polyatomic ion made up of a hydrogen and oxygen atom bonded together in a covalent bond. Its chemical formula is OH-. Many hydroxides are basic. The hydroxides of the alkali metals and the alkaline earth metals are strong bases. Most of the transition metal hydroxides are insoluble. Sodium hydroxide, the most common hydroxide, is made by electrolysis of a solution of sodium chloride.

The negative charge makes the compound highly reactive with many substances, especially cations. In nature, hydroxide can be found dissolved in water in. The compound on its own does not have many uses but other compounds containing hydroxide are essential. Called hydroxides, these compounds are used to manufacture an abundance of everyday items such as soap, paper, dye, and fabric.


Sodium hydroxide is often sold under the common name lye.
Potassium hydroxide, sold commonly as caustic potash, comes in white flakes.

Hydroxide is a diatomic molecule consisting of one oxygen atom covalently bonded with one hydrogen atom. It is a base, nucleophile (meaning it donates electrons in an ionic bond), and catalyst in many chemical reactions. Because of its negative charge, it is classified as a polyatomic ion. Its negative charge causes it to be extremely active when it contacts any cations, especially alkali metals and alkali earth metals, forming a variety of salts. Hydroxide, when exposed to air, reacts with carbon dioxide to form bicarbonate. Solutions containing the compound can react with the silicon in glass and break it down.[3]


Hydroxide is found dissolved in water. Though it is a small part of the dissolved substances in water, it is vital. Other compounds containing hydroxide are very common in nature. [3]

Hydroxides can be seen as hydrated oxides. Some metal oxides react with water to make metal hydroxides: Na2O + H2O --> 2 NaOH

Some examples of strong bases:

Formula Name Common name
LiOH Lithium hidroxide
NaOH Sodium hydroxide Caustic soda / Lye
KOH Potassium hidroxide Caustic potash
Ca(OH)2 Calcium hidroxide
Ba(OH)2 Barium hidroxide
Sr(OH)2 Strontium hidroxide


Sodium hydroxide, the most common hydroxide

Hydroxide on its own is not particularly useful. However, once bonded with other atoms, its compounds have many uses. One of the most common compounds containing hydroxide is sodium hydroxide. Sodium hydroxide, although extremely corrosive, is used often in manufacturing soaps, rayon, paper, explosives, dye, petroleum products, cotton fabric, laundering and bleaching, metal cleaning and processing, oxide coating, electroplating, and electrolytic extracting. Sodium hydroxide is even sold commercially in drain and oven cleaners.[4]

Another well known compound is potassium hydroxide. It is highly corrosive like sodium hydroxide. Potassium hydroxide is used in chemical manufacturing, petroleum refining, and cleaning compounds. Because it is a strong base, it is sold commercially in different forms such as pellets, flakes and powders. For food use, it is generally recognized as safe and is used as a pH control agent, stabilizer and thickener.[5] Potassium hydroxide is also used in alkaline batteries electrolytes.[6]

There are other uses for many existing hydroxides:

  • Caustic soda helps to control and remedy the acidic pollution of the environment. So it is used in various processes to control the acidity and neutralize acidic waste.


  1. National Center for Biotechnology Information. Hydroxide PubChem. Accessed 28 November 2017.
  2. 2.0 2.1 Hydroxide HMDB. Accessed 28 November 2017. Unknown Author.
  3. 3.0 3.1 Hydroxide Wikipedia. Accessed 28 November 2017. Unknown Author.
  4. National Center for Biotechnology Information. Sodium Hydroxide PubChem. Accessed 27 November 2017.
  5. National Center for Biotechnology Information. Potassium Hydroxide PubChem. Accessed 27 November 2017.
  6. Brown, Lawrence S.; Holme, Thomas A (2011). Chemistry for Engineering Students (2nd ed.). Belmont, CA: Brooks/Cole. p. 309. ISBN 978-1-4390-4791-0.