Hydroxide is a diatomic anion consisting of one atom of oxygen and hydrogen bonded together by a covalent bond, with chemical formula as \( small OH- \) and carries negatively charged ion. It functions as a nucleophile, a ligand, a catalyst, and a base.
Ion of a metal is usually the positively charged part of the compound, for example, aluminum, magnesium or sodium, and might be in the organic group. The inorganic hydroxides consist of alkali and alkali earth metals are important industrial alkalis like calcium hydroxide and sodium hydroxide.
The hydroxide attached to electropositive can ionize itself and liberate hydrogen cation \( small left (H+ ight )\) converting the parent compound as an acid. On the other hand, many of inorganic substance having the word hydroxide in their name are the covalent compound containing hydroxyl groups but not the ionic compounds of hydroxide ion.
Hydroxide Ion
Due to the self-ionization reaction, the hydroxide ion is a natural part of water.
\(H_{3}O^{+} + OH^{-} ightleftharpoons 2H_{2}O\)
While, the equilibrium constant of this reaction is defined as
\(K_{w} = left [H^{+} ight ] left [OH^{-} ight ]\)
Applications
The solutions of sodium hydroxide are widely used in the manufacture of paper, pulp, textiles, soaps, detergents, drinking water and drain cleaner. It is also known as caustic soda and lye. The primary method of manufacturing by the process of chlor-alkali.
The solution that contains hydroxide ion is obtained when weak acid salt is dissolved in water. The sodium carbonate is used as an alkali by the behavior of the hydrolysis reaction.
\(CO_{3}^{2-} + H_{2}O ightleftharpoons HCO_{3}^{-} + OH^{-}\)
Bauxite is the primary ore through which the metal is the manufacturer and is a basic of the hydroxide of aluminum. Similarly, lepidocrocite \( small left (gamma – FeOleft ( OH ight ) ight )\) and the goethite \( small left (alpha – FeOleft ( OH ight ) ight )\) are also the basis of hydroxide of ion and one among the ores that used to manufacture the metallic iron.
Inorganic Hydroxides
Alkali Metals
Apart from Sodium hydroxide \( small NaOH\) and potassium hydroxide \( small KOH\), the hydroxides of other alkali metals are also useful. The lithium hydroxide \( small pK_{b}\) of \( small -0.36\) is a strong base used in of breathing gas purification system for submarines and spacecraft to remove carbon dioxide \( small CO_{2}\) from exhaled gas.
\(2 LiOH + CO_{2} ightarrow Li_{2}CO_{3} + H_{2}O\)
Alkaline Earth Metals
The Beryllium hydroxide \(Beleft (OH_{2} ight )\) is amphoteric. The addition of acid provides a soluble hydrolysis products like trimeric ion \(small left [Be_{3}left (OH ight )_{3}left (H_{2}O ight )_{6} ight ]^{3+}\) which is hydroxy \(small left (OH ight )\) group.
Boron Group Elements
The boric acid is the simplest hydroxide of boron \(small Bleft (OH ight )_{3}\). Unlike, the alkaline earth hydroxides and alkali hydroxide, the boric acid doesn’t disconnect in aqueous solution. It reacts with molecules of water by releasing protons as Lewis acid.
\( B left (OH ight )_{3} + H_{2}O ightleftharpoons Bleft ( OH ight )_{4}^{-} + H^{+}\)
Carbon Group Elements
The carbon forms complex hydroxides. The hypothetical compound \(small Cleft (OH ight )_{4}\) like methanetetraol or orthocarbonic acid is unstable aqueous solutions.
\( C left (OH ight )_{4} ightarrow HCO_{3}^{-} + H_{3}O^{+}\)
\( HCO_{3}^{-} + H^{+} ightleftharpoons H_{2}CO_{3}\)
While, the carbon dioxide is also known as carbonic anhydride, which means that it is formed by dehydration of carbonic acid \(small H_{2}CO_{3} left (OCleft (OH ight )_{2} ight )\).
Other Main-Group Elements
The other main-group elements of hydroxide in inorganic hydroxides are sulfuric acid, xenic acid, telluric acid, phosphoric acid, ortho-periodic acid and phosphorous acid.
Hydroxide in Organic Reactions
Sodium hydroxide and potassium hydroxide are the two popular substance in organic chemistry.
Base Catalysis
The hydroxide ions in organic reactions act as a base catalyst. It abstracts a proton from a weak acid and the common substance for proton abstraction are carbon acids, amines phenols, and alcohols.
Nucleophilic Reagent
The hydroxide ion in nucleophilic is intermediate between the amido ion \(small left (NH- ight )\) and fluoride ion \(small left (F^{-} ight )\). The hydrolysis of an ester \(small R^{1}Cleft ( O ight )OR^{2} + H_{2}O ightleftharpoons R^{1}Cleft ( O ight )OH + HOR^{2}\) is an example of nucleophilic acyl.
