Copper(II) Sulfate (CuSO₄) — Properties, Uses & Safety

Overview

Copper(II) sulfate (CuSO4) is a transition metal salt with a molar mass of 159.61 g/mol, widely recognized for its striking blue color in its pentahydrate form (CuSO4 dot 5H2O), commonly called blue vitriol. The anhydrous form is a white to grayish powder that turns blue upon absorbing water — a classic test for the presence of water in chemistry laboratories. Copper sulfate is an ionic compound consisting of Cu2+ cations and SO4 2- anions arranged in a crystalline lattice. In the pentahydrate, four water molecules coordinate directly to the copper ion in a square planar arrangement, while the fifth bridges between sulfate groups through hydrogen bonding. This coordination chemistry gives the compound its vivid blue color, as the d-d electronic transitions in the Cu2+ ion absorb red-orange light. GHS hazard codes include H302 (harmful if swallowed), H400 (very toxic to aquatic life), and H410 (very toxic to aquatic life with long-lasting effects), reflecting its environmental toxicity to fish and aquatic organisms. Copper sulfate is used as a fungicide (Bordeaux mixture in agriculture), an algaecide for swimming pools and water reservoirs, a wood preservative, and in electroplating and electrorefining of copper. In the laboratory, it is a staple reagent for crystal growing experiments, flame tests producing a green-blue flame, and demonstrations of hydration and dehydration reactions. For chemistry students, copper sulfate is an exceptionally versatile teaching compound. Growing large, well-formed blue crystals from saturated solutions teaches supersaturation, crystallization, and patience. The reversible dehydration reaction demonstrates hydrated versus anhydrous salts and can be used to calculate waters of crystallization. The blue color introduces crystal field theory and d-orbital splitting in transition metal complexes. Copper sulfate also appears in displacement reactions such as Fe + CuSO4 yielding FeSO4 + Cu, illustrating the activity series of metals.

IUPAC Name

copper(2+) sulfate

CAS Number

7758-98-7

PubChem CID

24462

Molecular Formula

CuSO₄

Molar Mass

159.609 g/mol

State at STP

solid

Appearance

Blue crystalline solid (pentahydrate); white when anhydrous