Hydroxide

Hydroxide

Hydroxide is a diatomic anion consisting of one atom of oxygen and hydrogen bonded together by a covalent bond, with the chemical formula OH- and carries a negatively charged ion. It functions as a nucleophile, a ligand, a catalyst and a base.

The ion of a metal is usually the positively charged part of the compound, for example, aluminium, 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 the electropositive can ionise itself and liberate hydrogen cation (H+), converting the parent compound to an acid. On the other hand, many inorganic substances having the word hydroxide in their name are covalent compounds containing hydroxyl groups but not ionic compounds of hydroxide ions.

Hydroxide Ion

Due to the self-ionisation reaction, the hydroxide ion is a natural part of water.

\(\begin{array}{l}H_{3}O^{+} + OH^{-} \rightleftharpoons 2H_{2}O\end{array} \)

While the equilibrium constant of this reaction is defined as

\(\begin{array}{l}K_{w} = [H^{+}] [OH^{-}]\end{array} \)

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 a hydroxide ion is obtained when weak acid salt is dissolved in water. The sodium carbonate is used as an alkali by the behaviour of the hydrolysis reaction.

\(\begin{array}{l}CO_{3}^{2-} + H_{2}O \rightleftharpoons HCO_{3}^{-} + OH^{-}\end{array} \)

Bauxite is the primary or through which the metal is the manufacturer and is a basic of hydroxide of aluminium. Similarly, lepidocrocite γ – FeO(OH) and the goethite α– FeO (OH) are also the basis of the hydroxide of ions and one among the ores that are used to manufacture metallic iron.

Inorganic Hydroxides

Alkali Metals

Apart from sodium hydroxide NaOH and potassium hydroxide KOH, the hydroxides of other alkali metals are also useful. The lithium hydroxide pK_b of -0.36 is a strong base used in the breathing gas purification system for submarines and spacecraft to remove carbon dioxide CO₂ from exhaled gas.

\(\begin{array}{l}2 LiOH + CO_{2} \rightarrow Li_{2}CO_{3} + H_{2}O\end{array} \)

Alkaline Earth Metals

The beryllium hydroxide Be(OH₂) is amphoteric. The addition of acid provides a soluble hydrolysis product like trimeric ion [Be₃(OH)₃(H₂O)₆]³⁺, which is the hydroxy (OH) group.

Boron Group Elements

Boric acid is the simplest hydroxide of boron B(OH)₃. Unlike alkaline earth hydroxides and alkali hydroxides, boric acid doesn’t disconnect in an aqueous solution. It reacts with molecules of water by releasing protons as Lewis acid.

\(\begin{array}{l} B (OH)_{3} + H_{2}O \rightleftharpoons B (OH)_{4}^{-} + H^{+}\end{array} \)

Carbon Group Elements

The carbon forms complex hydroxides. The hypothetical compound C(OH)_4, like methanetetraol or orthocarbonic acid, is an unstable aqueous solution.

\(\begin{array}{l} C (OH)_{4} \rightarrow HCO_{3}^{-} + H_{3}O^{+}\end{array} \)

\(\begin{array}{l} HCO_{3}^{-} + H^{+} \rightleftharpoons H_{2}CO_{3}\end{array} \)

While carbon dioxide is also known as carbonic anhydride, which means that it is formed by the dehydration of carbonic acid H₂CO₃(OC(OH)₂).

Other Main-group Elements

The other main-group elements of hydroxide in inorganic hydroxides are sulphuric 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 substances 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 substances for proton abstraction are carbon acids, amines phenols and alcohols.

Nucleophilic Reagent

The hydroxide ion in nucleophilic is intermediate between the amido ion (NH-) and fluoride ion F^–. The hydrolysis of an ester

\(\begin{array}{l}R^{1}C(O)OR^{2} + H_{2}O \rightleftharpoons R^{1}C (O)OH + HOR^{2}\end{array} \)

is an example of nucleophilic acyl.

Frequently Asked Questions on Hydroxide

What is the chemical formula of a hydroxide?

Hydroxide is a diatomic anion with the chemical formula OH^–.

Which ions are released on the dissociation of water?

Protons and hydroxide anions are released during the dissociation of water.

Give the reaction between sodium carbonate and water.

Sodium carbonate reacts with water to give bicarbonate anion and hydroxide anion.
CO₃^2- + H₂O → HCO₃^– + OH^–.

Which salt is formed by the reaction of lithium hydroxide with carbon dioxide?

Lithium carbonate is formed by the reaction of lithium hydroxide with carbon dioxide.