Ferrous sulfate, also known as iron(II) sulfate, can be classified into different main forms based on its hydration state and physical properties. The main classifications are:

1. Ferrous Sulfate Heptahydrate (FeSO4·7H2O):

This is the most common and widely recognized form of ferrous sulfate.

It consists of seven water molecules per formula unit.

Appearance: Bright blue-green crystals or powder.

Solubility: Highly soluble in water, forming a greenish solution.

Uses: Used in agriculture as a fertilizer additive, in water treatment, as a nutritional supplement (iron supplement), and in various industrial applications including the production of iron salts, pigments, and chemicals.

2. Ferrous Sulfate Monohydrate (FeSO4·H2O):

Contains one water molecule per formula unit.

Appearance: Pale green crystals or powder.

Solubility: Soluble in water, forming a greenish solution.

Uses: Primarily used as a nutritional supplement in iron supplements and food fortification, in agriculture as a fertilizer, in water treatment, and in industrial applications such as pigment production and chemical synthesis.

3. Anhydrous Ferrous Sulfate (FeSO4):

Contains no water molecules in its crystal structure.

Appearance: Typically a pale green to white crystalline solid.

Solubility: Soluble in water, forming a colorless solution.

Uses: Used in various industrial processes, water treatment, pigment production, and chemical synthesis.

These classifications are based on the hydration state of the ferrous sulfate molecule, which affects its physical properties such as appearance and solubility, as well as its specific applications in different industries and fields