Aluminium Sulfate Octadecahydrate

Aluminium sulfate octadecahydrate is a chemical compound with the formula Al2(SO4)3•18H2O. It is also known as alum or papermaker's alum. The compound is a white crystalline solid that is highly soluble in water.

The structure of aluminium sulfate octadecahydrate consists of two aluminium ions (Al3+) and three sulfate ions (SO42-) arranged in an octahedral shape. The aluminium ions are surrounded by six water molecules, while the sulfate ions are surrounded by four water molecules each. The remaining water molecules are not directly coordinated to any ions but are held in the crystal lattice through hydrogen bonding.

Aluminium sulfate octadecahydrate has many applications, including as a coagulant in water treatment and as a mordant in dyeing textiles. It is also used in the paper industry to improve the retention of dyes and pigments on paper fibers. Additionally, it has uses in the food industry as a firming agent, and in pharmaceuticals as an astringent.

When aluminium sulfate octadecahydrate is dissolved in water, it dissociates into its constituent ions, Al3+ and SO42-. These ions can then react with other molecules in the solution, leading to various chemical processes. For example, in water treatment, the Al3+ ions can react with suspended particles to form larger clumps, which can then be more easily removed from the water. In textiles, the mordant properties of the compound allow dyes to bind more tightly to the fabric, resulting in a brighter and longer-lasting color.