Hydroxide - (OH⁻)

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What is Hydroxide?

Hydroxide is a diatomic anion having the chemical formula OH. Hydroxide is also referred to as either Hydroxyl radical or Hydroxyl or hydroxide ion. It is comprised of an oxygen and hydrogen atom, that is held together by a covalent bond. The hydrogen atom carries a negative electric charge. It can be used widely as a food preservative, for urine alkalization to prevent kidney stones, which is an anticoagulant for stored blood, and the buffer. It also acts as a catalyst, a ligand, a nucleophile, and a base.

The ion produces salts, where a few of them dissociate in an aqueous solution to liberate solvated hydroxide ions, and it is a minor water constituent. When a strongly electropositive center and the hydroxide are attached to each other, hydroxide can ionize itself to liberate a cation of hydrogen and makes the parent compound an acid.

HO, which is an electrically neutral compound, is given as the hydroxyl radical. –OH, the covalently-bound group is given as the hydroxy group. The hydroxide ion and hydroxy groups are nucleophiles and function as catalysts in organic chemistry.

Let us look at the important properties of hydroxide.

Hydroxide Properties



Hydroxide Chemical Formula


Monoisotopic mass of Hydroxide

17.003 g/mol

Molecular Weight of Hydroxide

17.007 g/mol

Conjugate acid


Conjugate Base

Oxide anion

Hydroxide Structure (OH)

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Applications of Hydroxide

Sodium hydroxide solutions, which are also known as lye and caustic soda, can be used in the manufacturing of pulp and paper, textiles, drinking water, soaps and detergents, and also as a drain cleaner. The worldwide production, according to 2004 was approximately 60 million tonnes. The principal method of manufacture is given as the chloralkali process.

Solutions that contain the hydroxide ion are produced when a salt of a weak acid is dissolved in water. Sodium carbonate can be used as an alkali, for example, by the hydrolysis virtue reaction.

Although the sodium carbonate solution's base strength is lower compared to the concentrated sodium hydroxide solution, it has the advantage of being solid. It can also be manufactured on a vast scale (in 2005 - 42 million tonnes) by Solvay's process. An example of sodium carbonate used as an alkali is washing a soda (alternate name for sodium carbonate), which acts on the insoluble esters, like triglycerides, commonly known as fats hydrolyze and make them soluble.

Bauxite, which is basic aluminium hydroxide, is the principal ore from which the metal is manufactured. In the same way, lepidocrocite (γ-FeO(OH)) and goethite (α-FeO(OH)), basic hydroxides of iron, which are among the principal ores, that can be used for the manufacture of metallic iron. Other numerous uses can be found in many individual hydroxides.

pH of Hydroxide

When the pH of a solution is less than 7, the solution is considered acidic. In contrast, the solution is neutral if it is roughly 7. Moreover, the solution is considered to be fundamental if the pH is greater than 7. Then, for an acidic solution, the hydrogen ion concentration is higher than the hydroxide ion concentration.

Hydroxide Formation

The most prevalent hydroxide formation method is given as the hydration reaction of a few alkali and rare-earth metals. For example, to get sodium hydroxide, we have to add metallic sodium into the water, which is chemically represented as follows.

2Na + 2H2O → 2NaOH + H2

To get the other metal's hydroxide that does not react directly with water, which is an exchange reaction (metathesis), is normally used as equated below.

CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4

Valancy of Hydroxide

Hydroxide ion, an OH compound, is made of both hydrogen and oxygen atoms. Prior to knowing the valency of an atom, we are required to understand the electronegativity concept. Oxygen is a more electronegative atom to of hydrogen. Thus, the oxygen atom carries a charge of -2, whereas the hydrogen atom carries a charge of +1. Therefore, OH has an overall charge of -1.

Some Common Uses of Hydroxide

In general, when we speak about hydroxides, it reminds us of bases and alcohol.

Let us look at the common uses of Hydroxide.

  • Hydroxides are proton acceptors in bases: They receive protons or hydrogen ions from acids for the formation of water. The equation for this is the easiest way to represent a neutralization reaction, which can be given as, H+ + OH- → H2O.

  • The hydroxide radicals can also be found in other organic compounds such as sugars (fructose, glucose, starch, and more), Soap, and Lipids(Fats). Furthermore, we all know their differential protective and useful purposes.

  • A few hydroxides like Slaked lime Ca(OH)2 can be used to prepare Calcium carbonate (CaCO3) and ammonia.

  • The other basic solutions absorb acidic gases like carbon dioxide and sulfur dioxide, thereby cleaning the air in its vicinity.

Did You Know?

  • Hydroxide exists alone when it is in water because acids and bases can neutralize each other in the solution. It is essential to differentiate between H2O and HO in reactions.

FAQ (Frequently Asked Questions)

1. Explain if Hydroxide an Acid?

Answer: The solution is acidic if one of those ions is H. The strong acid hydrogen chloride (otherwise called HCl) is an example, whereas the solution is basic if one of the ions is OH-. Sodium hydroxide (NaOH) is one of the examples of such a solid base.

2. Is Hydroxide Harmful?

Answer: The concrete and its solutions are corrosive. Sodium hydroxide is odourless; therefore, the odour does not turn into dangerous concentrations. Also, sodium hydroxide does not form systemic toxicity. However, it is very corrosive and can also cause extreme burns in all tissues with which it comes into contact.

3. Why is the Hydroxide Negatively Charged?

Answer: In this compound, 2 electrons share oxygen bonds with hydrogen. Hydroxide carries a negative charge because an electron has been accepted. Moreover, the oxygen is depicted as O, which is bound to the hydrogen, depicted as H. Hence, we can see that the negative sign is the product's most negative component.