Copper Sulfate – Properties and Reactions

Appearance:
Vibrant blue solid crystals, or a white crystalline powder depending on the amount of water contained in its structure.

Odor:
Odorless.

Molar Mass:
• CuSO₄ (anhydrous): 159.61 g/mol
• CuSO₄·5H₂O (pentahydrate): 249.68 g/mol

Density:
2.286 g/cm³.

Solubility:
Highly soluble in water.
At 20 °C, approximately 23.1 g dissolves in 100 mL of water, forming an acidic solution.
Solubility increases with temperature.
Also soluble in methanol and glycerol.
Insoluble in non-polar solvents such as benzene.

Melting / Decomposition Point:
Decomposes at approximately 110 °C, losing its water of hydration.

Crystal System

Triclinic.

Chemical Formula
• Anhydrous: CuSO₄
• Pentahydrate: CuSO₄·5H₂O

Stability

Stable under normal conditions.

Hygroscopicity

The anhydrous form is highly hygroscopic and readily absorbs moisture from the environment to form the pentahydrate.

Boiling Point (Anhydrous CuSO₄)

Reported decomposition at approximately 650 °C.

⸻

Reactions

Reaction with heat
• Between 88–100 °C, it loses its water of crystallization:
CuSO₄·5H₂O → CuSO₄ + 5H₂O
• At 650 °C, it decomposes further to produce copper oxide and sulfur dioxide:
2CuSO₄ → 2CuO + SO₂ + SO₃

Reaction with Active Metals

Copper sulfate reacts with more active metals such as iron, producing metallic copper:
CuSO₄ + Fe → FeSO₄ + Cu

Reaction with Bases (Alkalis)

With sodium hydroxide, it forms blue copper(II) hydroxide:
CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄

Reaction with Iodide Ions

Copper(II) ions are reduced by iodide, forming white copper(I) iodide and iodine:
2Cu²⁺ + 4I⁻ → 2CuI(s) + I₂

Reaction with Ammonia

Initially forms copper hydroxide; in excess ammonia, it forms the deep-blue tetraamminecopper(II) complex:
Cu(OH)₂ + 4NH₃ → [Cu(NH₃)₄]²⁺ + 2OH⁻

Redox Behavior

Cu²⁺ ions give copper sulfate oxidizing properties. It is used in numerous redox-based analytical procedures, including tests for reducing sugars.

Reaction with Concentrated Hydrochloric Acid

Forms tetrachlorocuprate(II) complexes:
CuSO₄ + 4Cl⁻ → [CuCl₄]²⁻ + SO₄²⁻