Copper Sulfate

Brilliant blue crystals for electrochemistry and crystal growing

Molecular structure

Formula: CuSO₄·5H₂O — Copper(II) sulfate pentahydrate, cupric sulfate, blue vitriol, bluestone
Appearance: Brilliant blue crystalline solid
Hazard: Harmful · Irritant · Environmental hazard

Properties

Brilliant blue crystalline solid when hydrated; white/gray when anhydrous. The blue color comes from copper coordinating with water molecules. Used in electroplating, as a fungicide, and in crystal growing. Related to other copper salts and can be converted to copper carbonate, oxide, or metal through various reactions.

Historical Context

“Blue vitriol” was known to ancient civilizations. The Egyptians used copper compounds for eye treatments (not recommended!), and medieval alchemists considered it one of the seven “vitriols” - metal sulfates essential to their work. The word “vitriol” comes from Latin vitrum (glass), describing the glassy appearance of the crystals.

Copper sulfate played a crucial role in the development of electrochemistry. In 1800, shortly after Volta announced his electric pile, William Cruickshank used copper sulfate solutions to electrodeposit copper, pioneering electroplating. John Daniell’s 1836 battery used copper sulfate as the cathode electrolyte, providing the first reliable source of steady electrical current.

The compound saved European vineyards in the 1880s when Pierre-Marie-Alexis Millardet discovered that a mixture of copper sulfate and lime (Bordeaux mixture) controlled downy mildew, which was devastating French wine production.

Experiments

Crystal Growing: Grow stunning blue triclinic crystals - some of the most beautiful and easily-grown crystals. Demonstrates crystal structure, hydration, and coordination chemistry. The deep blue color comes from copper’s coordination with water molecules. Growing copper sulfate crystals

Electroplating: Use as electrolyte to copper-plate objects - connect copper electrodes to a battery with the object as cathode. Demonstrates electrochemistry and reduction-oxidation reactions. Can plate keys, coins, or other conductive objects.

Experiments using this chemical:

Safety

Warning

Moderate hazard — harmful; toxic to aquatic life.

Incompatible with: Strong bases (copper hydroxide precipitation); reactive metals such as iron, zinc, magnesium (displacement reactions — the intended chemistry in some experiments); acetylene (explosive copper acetylide); hydroxylamine