COPPER SULFATE (CUSO4): STRUCTURE, PROPERTIES, OBTAINING, USES - CHEMISTRY - 2025

The copper sulfate is an inorganic compound consisting of the elements copper (Cu), sulfur (S) and oxygen (O). Its chemical formula is CuSO ₄. Copper is in the oxidation state +2, sulfur +6, and oxygen has a valence of -2.

It is a white solid that, when exposed to humidity in the environment, becomes its blue pentahydrate CuSO _{4 •} 5H ₂ O. The white solid is obtained by heating the blue to eliminate water.

Anhydrous copper sulfate (CuSO ₄) (without water in its crystalline structure). W. Oelen / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

It has been used as an antibacterial agent for centuries to heal wounds in humans and animals. It also works as a fungicide, as an astringent, an antidiarrheal and to control intestinal diseases in animals. It is also used as an antifungal agent in plants.

However, some of its uses have been discontinued because its excess can be toxic to humans, animals and plants. The concentration range in which it can be used is narrow and depends on the species.

It is used as a catalyst in chemical reactions and as a desiccant for solvents. It allows to improve the resistance and flexibility of some polymers.

Excessive amounts of this compound can be harmful in soils, as it is toxic to microorganisms that are beneficial to plants.

Structure

Copper sulfate is made up of a copper ion (Cu ²⁺) and a sulfate ion (SO ₄ ^2-).

Ionic structure of copper (II) sulfate. Author: Marilú Stea.

Due to the loss of two electrons, the copper (II) ion has the following electronic conformation:

1s ² 2s ² 2p ⁶ 3s ² 3p ⁶ 3d ⁹

It can be seen that it has the incomplete 3d orbital (it has 9 electrons instead of 10).

Nomenclature

• Anhydrous copper sulfate
• Copper (II) sulfate
• Cupric sulfate

Properties

Physical state

White or greenish-white solid in the form of crystals.

Molecular weight

159.61 g / mol

Melting point

At 560 ° C it decomposes.

Density

3.60 g / cm ³

Solubility

22 g / 100 g of water at 25 ° C. Insoluble in ethanol.

Chemical properties

When subjected to air humidity below 30 ° C, it becomes the pentahydrate compound CuSO _{4 •} 5H ₂ O.

Its aqueous solutions are blue due to the formation of the hexaacuocopper (II) ²⁺ ion which produces said coloration. In this ion two of the water molecules are further away from the metal atom than the other four.

Deformed structure of the hexaacuocopper (II) ²⁺ ion. Benjah-bmm27 / Public domain. Source: Wikimedia Commons.

This is due to the so-called Jahn-Teller effect, which predicts that this type of system will experience the distortion caused by the fact that Cu ²⁺ has an electronic structure that ends in d ⁹, that is, an incomplete orbital (it would be complete if would be d ¹⁰).

If ammonia (NH ₃) is added to these solutions, complexes are formed in which NH ₃ successively displaces the water molecules. They are formed for example from ²⁺ to ²⁺.

When CuSO ₄ is heated to decomposition, it emits toxic gases and turns into cupric oxide CuO.

Obtaining

Anhydrous copper sulfate can be obtained by total dehydration of the pentahydrate compound, which is achieved by heating it until the water molecules evaporate.

CuSO _{4 •} 5H ₂ O + heat → CuSO ₄ + 5 H ₂ O ↑

The pentahydrated compound is blue, so when the water of crystallization is lost, the white anhydrous CuSO ₄ is obtained.

Applications

Some of its uses overlap with that of the pentahydrate compound. Others are specific to the anhydrous substance.

As an antibacterial agent

It has potential as an antimicrobial agent. It has been used for thousands of years, including in South and Central American cultures, to prevent wound infection by means of gauze soaked in a solution of this compound.

It is estimated that in the mechanism of their antibacterial activity Cu ²⁺ ions form chelates with enzymes that are crucial for the cellular functions of bacteria, deactivating them. They also induce the formation of hydroxyl radicals OH •, which damage the membranes of bacteria and their DNA.

CuSO ₄ can work against some pathogenic bacteria. Author: Gerd Altmann. Source: Pixabay.

It has recently been reported that traces of CuSO ₄ can increase the antimicrobial activity of natural products rich in polyphenols, such as extracts of pomegranate and infusions of some types of tea plants.

In veterinary applications

It is used as an antiseptic and astringent for mucous membranes and to treat conjunctivitis and external otitis. It is used to carry out therapeutic or prophylactic baths to avoid rotting of the legs of cattle, sheep and other mammals.

The aqueous solutions of CuSO _{4 are} used to cure the hooves of cattle. Authors: Ingrid und Stefan Melichar. Source: Pixabay.

It serves as a caustic agent for necrotic masses on the limbs of cattle, stomatitis ulcers and granular tissue of these. It is used as a fungicide in the treatment of ringworm and fungal diseases of the skin.

It is also used as an emetic (agent to induce vomiting) in pigs, dogs and cats; as an antidiarrheal astringent for calves and to control intestinal moniliasis in poultry and trichomoniasis in turkeys.

As a supplement in animal feed

Copper sulfate has been used as a supplement in very small amounts to feed cattle, pigs, and poultry. It is used to treat copper deficiency in ruminants. In the case of pigs and poultry it is used as a growth stimulant.

Copper has been identified as essential for mammalian hemoglobin biosynthesis, cardiovascular structure, bone collagen synthesis, enzyme systems, and reproduction.

As mentioned in the previous section it can also be given as a disease control medication. However, supplementation and / or medication levels should be closely monitored.

Poultry and their eggs can be affected by excess copper sulfate in their diet. Author: Pexels. Source: Pixabay.

From a certain amount, which depends on each species, growth decrease, loss of appetite and weight, damage to certain organs and even the death of animals can occur.

For example, in chickens, supplementation of 0.2% or more decreases their food intake with the consequent weight loss, decreased egg production and the thickness of their shells.

In agricultural applications

In organic production systems it is not allowed to use synthetic fungicides, only products based on copper and sulfur are accepted, such as copper sulfate.

For example, certain fungi that attack apple plants, such as Venturia inaequalis, are killed with this compound. Cu ²⁺ ions are thought to possibly be capable of entering the fungal spore, denaturing proteins, and blocking various enzymes.

Copper sulfate is used to combat some fungi that attack apples. Algirdas at lt.wikipedia / Public domain. Source: Wikimedia Commons.

Importance of copper in plants

The element copper is important in physiological processes of plants such as photosynthesis, respiration and defense against antioxidants. Both the deficiency of this element and its excess generate reactive oxygen species that are harmful to their molecules and structures.

The range of copper concentrations for optimal plant growth and development is very narrow.

Adverse effects on agriculture

When this product is used in excess in agricultural activities it can be phytotoxic, cause premature development of fruits and change their color.

Additionally, copper accumulates in the soil and is toxic to microorganisms and earthworms. This conflicts with the concept of organic agriculture.

Although CuSO ₄ is used in organic agriculture it can be harmful to earthworms. Author: Patricia Maine Degrave. Source: Pixabay.

In catalysis of chemical reactions

Anhydrous CuSO ₄ serves as a catalyst for various reactions of organic carbonyl compounds with diols or their epoxides, forming dioxolanes or acetonides. Thanks to this compound, reactions can be carried out under mild conditions.

Example of a reaction in which anhydrous CuSO ₄ acts as a catalyst. Author: Marilú Stea.

It has also been reported that its catalytic action allows to dehydrate secondary, tertiary, benzylic and allylic alcohols to their corresponding olefins. The reaction is carried out very simply.

The pure alcohol is heated together with the anhydrous CuSO ₄ at a temperature of 100-160 ° C for a time of 0.5-1.5 hours. This results in dehydration of the alcohol and the olefin is distilled pure from the reaction mixture.

Dehydration of an alcohol by anhydrous copper (II) sulfate. Author: Marilú Stea.

As a dehydrating agent

This compound is used in chemistry laboratories as a desiccant. It is used to dehydrate organic liquids such as solvents. It absorbs water, forming the pentahydrate compound CuSO _{4 •} 5H ₂ O.

When the white anhydrous CuSO ₄ absorbs water it converts to the blue pentahydrate compound CuSO ₄.5H ₂ O. Crystal Titan / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0). Source: Wikimedia Commons.

To improve polymers

Anhydrous CuSO ₄ has been used to improve the properties of certain polymers while allowing them to be recyclable.

For example, particles of the compound in acetone have been mixed with acrylonitrile-butadiene rubber in a special mill, trying to make the CuSO ₄ particles very small.

Copper sulfate improves the bonding points of the polymer, forming a mixture with high strength, hardness and surprising flexibility.

In discontinued therapeutic applications

In the past, copper sulfate solutions were used for gastric lavage when someone suffered from white phosphorous poisoning. However, the solution was promptly stirred to avoid copper poisoning.

Solutions of this compound were also used along with other substances for topical applications on phosphorous skin burns.

Sometimes they served in certain forms of nutritional anemia in children and in copper deficiency in subjects who received parenteral nutrition, that is, people who cannot feed themselves by mouth.

Certain eczema, impetigo, and intertrigo lotions contained CuSO ₄. The solutions were used as an astringent in eye infections. Sometimes the crystals were applied directly to burns or ulcers.

All these applications are no longer carried out due to the toxicity that excess of this compound can induce.

References

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