What Is the Colour of Freshly Prepared FeSO₄ Solution?

Freshly prepared ferrous sulphate (FeSO₄) solution is blue-green in color. This distinctive hue is due to the presence of Fe²⁺ ions in the solution.

Why Is the Color Blue-Green?

• Fe²⁺ Ions: The ferrous (Fe²⁺) state imparts a blue-green color to the solution. This color is a result of the specific way Fe²⁺ ions interact with water molecules and absorb light.
• Oxidation Sensitivity: FeSO₄ is sensitive to oxidation. When exposed to air, Fe²⁺ ions can oxidize to Fe³⁺, forming ferric sulphate, which is yellow-brown in color. Therefore, the blue-green color is only observed in freshly prepared solutions that haven't been exposed to oxygen for long.

Practical Importance

• Analytical Chemistry: Fresh FeSO₄ is used in tests like the brown ring test for nitrates, which requires active Fe²⁺ ions for accurate results.
• Medical Use: Ferrous sulphate is also used as an iron supplement in medicine.

Key Takeaways

• Color: Blue-green for fresh solutions; turns brownish on oxidation.
• Reason: Presence of Fe²⁺ ions and their interaction with water.