Copper(II) sulfate

Cu 1
S 1
O 4

Formula unit Lattice

Choose Lattice to see three unit cells. Then drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

6 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; copper(II) sulfate has no molecular shape.

IUPAC name: copper sulfate
Molar mass: 159.602(27) g/mol
Atoms: 6
SMILES: [O-]S(=O)(=O)[O-].[Cu+2]
InChIKey: ARUVKPQLZAKDPS-UHFFFAOYSA-L
PubChem CID: 24462

Made of

Cu S O

Copper(II) sulfate usually goes to work as blue vitriol, a deep blue crystal that carries water inside its lattice. US food regulations give that form’s formula as CuSO₄·5H₂O, the pentahydrate. It is a hydrate, one of the many salts whose crystal lattices take up water molecules. With the water gone, the anhydrous salt remains, a greyish-white to greenish-white powder or crystal.

The anhydrous compound is built from copper, sulfur and oxygen, as a Cu²⁺ ion and a sulfate ion, SO₄²⁻. Its molar mass, 159.60 g/mol, belongs to that dry salt alone, and its IUPAC name is plain copper sulfate. It dissolves freely in water but not in ethanol. The Haz-Map occupational health database lists it as a fungicide, algaecide and herbicide, and as a micronutrient for fertiliser and animal feed. It also goes into electroplating solutions, leather tanning and titrations.

Structure and bonding

The drawing is the anhydrous salt, one formula unit of its ionic lattice: a copper ion marked 2+ and a sulfate ion, with no line between them. In the drawing, sulfur holds two oxygen atoms by double bonds and two by single bonds, and the ion’s two negative charges sit on the singly bonded pair. The real ion’s measured bonds are described on the calcium sulfate page. The pentahydrate’s crystals hold five water molecules for every CuSO₄, and none is drawn.

The Lattice view draws the anhydrous salt as three unit cells, from a structure measured at 100 K (−173 °C). Each cell holds 4 copper ions and 4 sulfate ions. Coordination picks out one copper ion and its 6 nearest oxygen atoms, one in each of 6 sulfate ions, 1.92 to 2.36 Å away. Those crystals are rhombic, according to the Hazardous Substances Data Bank (HSDB); the blue pentahydrate’s are triclinic in US food rules. Chem1 cautions that transition-metal salts such as copper(II) chloride often do not form truly ionic solids.

In water the copper becomes Cu²⁺(aq), a hexaaquo complex ion in Chem1’s description, with water molecules bonded directly to it, and the solution is acidic.

Where it turns up

Blue copper sulfate crystals go into ponds to keep algae down, the Agency for Toxic Substances and Disease Registry notes. Copper algaecides as a group work in aquaculture facilities, drainage canals and ditches, fountains, lakes and reservoirs, by the US Environmental Protection Agency’s (EPA) account. On dairy farms, cattle step through copper sulfate baths that guard against foot infections, and the spent bath water often ends up irrigating corn and alfalfa.

Around homes, copper serves as a garden and lawn fungicide. The pentahydrate also goes into sewer root killers for homeowners, products banned in a number of California counties and some in New York. US food rules allow the salt as a nutrient supplement and a processing aid, infant formula included, and list it among trace minerals added to animal feeds.

Why it matters

Copper’s first recorded use as a fungicide, on the EPA’s account, came in the mid-1700s, when cereal seed was treated with copper sulfate pentahydrate against stinking smut, or bunt. In the 1880s Pierre Marie Alexis Millardet, a French scientist, found copper effective against a broad range of fungi. The finding came from Bordeaux mixture, copper sulfate and water with hydrated lime. Farm copper pesticides, whatever their form, all yield the cupric ion, Cu²⁺, the active part. A copper pesticide was first registered in 1956, and EPA Registration Standards for copper sulfate followed in March 1986.

Copper sulfate is the most used copper compound in the United States, HSDB records. In 1984 industry took 52 per cent, wood preservation and chemical manufacture among its uses, and farming 48 per cent. In algae, copper makes the cell membrane leak its contents. Copper is also registered against freshwater snails that can carry harmful parasites, and HSDB traces its effect on molluscs to a block in their metabolism.

Properties

Properties of copper(II) sulfate Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 24462.
Property	Value	Unit	Source
Formula (Hill order)	CuO₄S
Molar mass	159.602(27) g/mol	g/mol	IUPAC/CIAAW 2024
Copper atoms	1
Sulfur atoms	1
Oxygen atoms	4
PubChem molecular weight	159.61 g/mol	g/mol	PubChem

Safety

Copper(II) sulfate irritates the eyes, the skin and the respiratory tract, and it is very toxic to aquatic life. Exposure could cause haemolysis, the breakdown of red blood cells, and harm to the kidneys and liver, the International Chemical Safety Card warns. Heated to decomposition, it gives off toxic sulfur oxide fumes. The PubChem Laboratory Chemical Safety Summary lists its classifications, and NIOSH, the US National Institute for Occupational Safety and Health, sets a workplace exposure limit for copper compounds.

Questions

What is blue vitriol?

Jefferson Lab gives blue vitriol as a name for hydrated copper sulfate, used as a farm poison, an algae killer in water treatment and a blue colouring for inks. Copper sulfate is usually used as a hydrate: US food regulations give it as the pentahydrate, CuSO₄·5H₂O. It comes as large deep blue crystals, blue granules or a light blue powder.

What is anhydrous copper sulfate?

It is the white salt left when heat drives the water out of the blue crystals. In moist air below 30 °C the change runs backwards, the Hazardous Substances Data Bank records: the white powder takes up water and becomes the pentahydrate again. The anhydrous salt also serves to detect and remove traces of water in alcohols and other organic compounds.

Is copper sulfate harmful to fish?

Yes. Copper binds rapidly to fish gill membranes, the EPA explains, damaging them and disrupting osmoregulation, the fish's control of water and salts in its body. European rules class copper(II) sulfate as very toxic to aquatic life, with lasting effects. In alkaline, carbonate-rich water, the US Fish and Wildlife Service notes, copper soon settles out as copper carbonates. In acidic water short of carbonates it stays active for a very long time.

What happens when zinc is put in copper sulfate solution?

Copper metal forms and the zinc is oxidised, giving up electrons. In Chem1's account, those electrons fall from the zinc to a lower free energy on the dissolved Cu²⁺ ions, free energy being the energy available to drive a change. Taking them up reduces the copper ions to the metal.