Hydroxide

Introduction

Hydroxide is a negatively charged diatomic ion. It combines with positively charged metals like sodium, magnesium, aluminium, etc. It also merges with organic compounds like ethyl, methyl, and aromatic rings. The name of the compound is represented by the prefix or suffix of the molecule. For Example, when it is attached to metal sodium it forms sodium hydroxide. When it combines with ethane, it forms ethyl alcohol.

What is Hydroxide?

A Hydroxide ion is a combination of hydrogen and an oxygen atom held together by a covalent bond. It is a negatively charged ion, also known as hydroxyl ion or oxidanide. It acts as a base, catalyst, ligand, and nucleophile in a chemical reaction. It is used widely in industries as a preservative, anticoagulant, and alkalization. It is the conjugate base of a water molecule. It is one of the simplest diatomic anions. It is found in several mineral ores in nature such as Limonite, Bauxite, etc.

Hydroxide ion

What is the relationship between 𝑶𝑯− and 𝑯+?

In the hydroxide ion, oxygen is more electronegative than hydrogen. When they form a covalent bond, the oxygen pulls the electron towards itself and generates a partial negative charge on the molecule 𝑂𝐻−. This attracts the positive 𝐻+ ion from water or in an acidic medium to form a hydronium ion.

• They form water molecules as the concentration of 𝐻+ ion and hydroxide ion 𝑂𝐻− is the same. They attract each other and form a water molecule.

• The concentration of hydroxide ion measures the pH of a solution.

Formation of Hydronium Ion

Sodium Hydroxide Formula

Sodium hydroxide is a white crystalline solid. Its chemical formula is 𝑁𝑎𝑂𝐻. It is formed by sodium cation 𝑁𝑎+ and hydroxide anion 𝑂𝐻− It is a widely used alkali for industrial and laboratory purposes like a cleaner, soap making, explosives, paper industry, etc. It is also known by the name Caustic Soda or Lye.

Sodium Hydroxide Structure

Sodium hydroxide is formed by the ionic bond of sodium ion and hydroxide ion. It is a neutral molecule, but its monohydrate forms an orthorhombic crystal structure. In this, sodium is encircled by three atoms of hydroxy ions and a water molecule.

Structure Sodium Hydroxide

Sodium hydroxide Preparation

The sodium hydroxide is prepared by various methods like electrolysis of mercury cell, chloralkali process, brine solution in Diaphragm, or mercury cell.

• Formation of sodium hydroxide by the Electrolysis of Brine Process − In this process, the Brine i.e., 𝑁𝑎𝐶𝑙 solution is electrolyzed in a diaphragm cell. The cell contains both cathode and anode.

• The water is reduced at the cathode rod and forms hydrogen gas and hydroxide ion.

$$\mathrm{2H_{2}O\:2e^{-}\rightarrow\:H_{2}\:+\:2OH^{-}}$$

• At the anode rod, the brine 𝑁𝑎𝐶𝑙 is broken into chlorine 𝐶𝑙− and Sodium-ion 𝑁𝑎+.

• In this process, chlorine and hydrogen can combine and cause an explosion so to avoid their reaction the cathode rod is combined with the porous diaphragm of asbestos.

• Later, sodium and hydroxide combine to form sodium hydroxide.

• The chlorine and hydrogen gas were later purified and compressed in a cylinder.

$$\mathrm{2Na\:+\:2OH^{-}\:\rightarrow\:2NaOH}$$

• Some side products are also formed in this reaction i.e., sodium metal, which was amalgamated by mercury at the cathode.

$$\mathrm{Na(aq)\:e^{-}\:+\:xHg(l)\rightarrow\:NaHg_{x}(l)}$$

• In this process, 50% sodium hydroxide produced in solution is removed directly and further dried and removed in crystalline form $\mathrm{NaOH.H_{2}O}$.

Preparation of Sodium Hydroxide

Physical and Chemical Properties

Physical Properties:

Physical Properties	Attributes
Colour	White
Appearance	Crystalline
Chemical Formula	$\mathrm{NaOH}$
Odour	Odourless
Density	2.13 g/cm3
Solubility	Soluble in water, glycerol, and insoluble in ether.
Boiling Point	1388°C
Melting Point	318°C

Chemical Properties:

• Reaction with Acids − When it reacts with acids it forms salt and water.

$$\mathrm{NaOH(aq)\:+\:HCl(aq)\:\rightarrow\:NaCl(aq)\:+\:H_{2}O(l)}$$

• Reaction with Metals − When sodium hydroxide is reacted with metals at a high temperature it forms metal oxides and releases hydrogen gas and sodium.

$$\mathrm{4Fe\:+\:6NaOH\rightarrow\:2Fe_{2}O_{3}\:+\:3H_{2}\:+\:6Na}$$

• Reaction with Acidic Oxides − When reacts with acidic oxides carbon dioxide, it forms sodium carbonate and water. It is an exothermic reaction.

$$\mathrm{2NaOH\:+\:CO_{2}\rightarrow\:Na_{2}CO_{3}\:+\:H_{2}O}$$

Uses of Sodium Hydroxide

• Hydroxides of metals are insoluble in water, but sodium hydroxide is not so it is used for the treatment of water, it precipitates metal hydroxides like aluminium hydroxide.

$$\mathrm{6NaOH(aq)\:+\:{Al_{2}}_{3}(aq)\rightarrow\:2Al(OH)_{3}(s)\:+\:3Na_{2}SO_{4}(aq)}$$

• Sodium hydroxide slowly reacts with glass and forms sodium silicate

• It is used in the saponification process to form detergents.

• Chlorine bleach is prepared by combining sodium hydroxide with chlorine.

• It is also used in the pharmaceutical industry in the preparation of medicines like anticoagulants, medicines, etc.

• It is used in fuel cells, as food preservatives, and in food processing.

Health Hazards associated with Sodium Hydroxide:

• It is highly corrosive and can cause severe burns in tissues.

• If exposed to sodium hydroxide solution or solid it can cause eye and skin irritation, and dermatitis.

• Eating or drinking sodium hydroxide can cause burns, vomiting, nausea, even death, etc.

Fun Facts

When we have to make a solution of sodium hydroxide, we always put solid sodium in the water not water on solid sodium hydroxide. When it dissolves in water it produces heat that is absorbed by water, not by sodium. If we pour water on solid sodium hydroxide it can cause burns.

Conclusion

Hydroxide is a negatively charged anion that is basic and has high pH. When it reacts with 𝐻+ions it neutralizes by forming an ionic bond. Mostly metal hydroxides are insoluble in water like copper(II) hydroxide, or hydroxide of iron but sodium hydroxide is water soluble. Sodium hydroxide is an inorganic compound. It is used for various commercial purposes like in the food industry, medicines, laboratories, etc.

FAQs

1. Why do Hydroxide ions exist alone in water?

Hydroxide is a negatively charged ion i.e., a base, and 𝐻+ion is a positive acid. The acid base reacts and neutralizes in the solution. So, hydroxide ions exit alone in the water.

2. What are the uses of hydroxide ions?

The hydroxide ion is a strong base and is used in many chemical reactions. For example, hydroxide of potassium is used in agriculture.

3. What is the use of sodium hydroxide in the paper industry?

The wood is first treated with a solution of sodium hydroxide and sodium sulphide. The unwanted material of the wood dissolves in solution and purifies the cellulose that is used to manufacture paper.

4. What is the role of sodium hydroxide in soil?

Sodium hydroxide is used to increase the pH of the soil.

5. Does Sodium hydroxide have antioxidant properties?

The sodium hydroxide extracted from the vegetation or soil has antioxidant properties.