Question

Why is alumina insoluble in water?

Answer 1

Alumina:

• Aluminium oxide, often known as alumina, is a chemical substance made up mostly of oxygen and aluminium molecules.
• It is a colourless crystalline substance that occurs naturally in a variety of forms, the most common of which is sapphire and ruby, both of which are made of corundum.
• Corundum is the most frequent crystalline form of alumina or aluminium oxide found in nature. Surprisingly, corundum may transform into sapphire and ruby gemstones under certain conditions.

Structure of Alumina:

Properties of Alumina:

• Alumina has good to excellent heat conductivity. It can tolerate strong acid and alkali attacks at extreme temperatures.
• It has very good dielectric qualities.
• Metallic Aluminum and oxygen in the atmosphere react quite quickly.
• High rigidity and strength are evident in it. It is offered with a purity level starting at 94% It cannot dissolve in water. Alumina can react with both acids and bases because it is an amphoteric material.
• Activated alumina is a granular, porous material. Excellent ceramic oxide is alumina that possesses great resistance to chemical and abrasive assaults.

Reason for alumina insoluble in water:

1. Aluminium oxide comes in a variety of shapes and sizes. It's an amphoteric oxide, which means it can form salts with both acids and bases. Corundum is another name for it (crystalline form).
2. Because of its hexagonal close packing (hcp) structure, aluminium oxide does not react with water at ambient temperature. Water cannot react with the oxide ions because they are bound together too tightly in the crystal lattice. When dissolved in water, it just settles.
3. Ionic compounds are made up of metals and non-metals. Aluminium oxide is therefore an ionic substance. Even so, it is water-insoluble.