COPPER SULFATE PENTAHYDRATE: STRUCTURE, PROPERTIES, USES - CHEMISTRY - 2025

The copper sulfate pentahydrate is an inorganic compound consisting of the elements copper (Cu), sulfur (S), oxygen (O) and water (H ₂ O). It contains copper (II) (Cu ²⁺) and sulfate (SO ₄ ^2-) ions. Its chemical formula is CuSO _{4 •} 5H ₂ O.

In nature it is found forming the mineral chalcantite or calcantite, also called chalclase or calclasse. It is a blue crystalline solid.

Crystal of copper sulfate pentahydrate CuSO _{4 •} 5H ₂ O. Author: Überraschungsbilder. Source: Wikimedia Commons.

It is used as a food supplement for some animals such as ruminants, pigs and poultry. In agriculture it serves as a pesticide. In mining activities it allows to recover other metals.

Due to its blue hue, it is used for coloring fabrics and metals. It has been used to deposit metallic copper on cellulose fibers to obtain electrically conductive fabrics. It is also used to prepare nanoparticles of copper and its oxides, with a variety of applications.

In high concentrations it can be toxic to fauna and flora, for this reason it is sometimes used to eliminate pests (animals or plants) from aquatic environments such as lagoons and natural ponds.

Structure

This compound is formed by the element copper in its oxidation state +2 and the sulfate anion. The latter has a sulfur atom with valence +6 surrounded by four oxygen atoms, each with valence -2. In this way, the sulfate ion has two negative charges.

It also has 5 water molecules in its structure. In the following figure you can see how the various atoms are arranged in the crystal.

Structure of CuSO _{4 •} 5H ₂ O. Author: Smokefoot. Source: Wikimedia Commons.

Cu ²⁺ (orange spheres) is coordinated simultaneously with 4 H ₂ O molecules (oxygen = red; hydrogen = white) and with 2 oxygen atoms of SO ₄ ^2- (sulfur = yellow). In the figure one of the H ₂ O molecules is in apparent freedom but is part of the crystalline structure.

Nomenclature

Chalcantite mineral CuSO _{4 •} 5H ₂ O. Author: Archaeodontosaurus. Source: Wikimedia Commons.

• Copper sulfate pentahydrate
• Copper (II) suffate pentahydrate
• Bluejack
• Blue stone (from English blue stone)
• Chalcantite, calcantite, chalclase or calclase

Properties

Physical state

Blue crystalline solid.

Molecular weight

249.686 g / mol

Melting point

Upon reaching 110 ºC, it decomposes.

Density

2,286 g / cm ³

Solubility

Soluble in water: 22.0 g / 100 g of water at 25 ° C. Soluble in methanol (CH ₃ OH). Slightly soluble in ethanol (CH ₃ CH ₂ OH).

Chemical properties

When this compound comes into contact with water, it dissolves forming the ions Cu ²⁺ and SO ₄ ^2-. Its solubility in water decreases significantly if sulfuric acid is present in the water.

H ₂ SO ₄ provides SO ₄ ^2- ions and its presence generates the “common ion” effect, since this ion is present in copper sulfate pentahydrate. Dissolution can be expressed like this:

CuSO _{4 •} 5H ₂ O (solid) + water ⇔ Cu ²⁺ + SO ₄ ^2- + water

Therefore, if the SO ₄ ^2- of sulfuric acid is already present in solution, the equilibrium shifts to the left, that is, towards the formation of the solid and thus the solubility decreases.

Obtaining

One of the ways to obtain copper sulfate pentahydrate is by dissolving the mineral malachite in aqueous sulfuric acid (H ₂ SO ₄) at a controlled temperature. Malachite contains Cu ₂ (OH) ₂ CO ₃ with other impurities, such as iron.

The impure copper (II) solution is treated with hydrogen peroxide (H ₂ O ₂) to ensure that the iron (II) (Fe ²⁺) impurities are converted to iron (III) (Fe ³⁺). The latter is precipitated in the form of ferric hydroxide (Fe (OH) ₃) using sodium hydroxide (NaOH).

Precipitating means that particles of an insoluble solid are formed in the solution, which falls to the bottom of the container that contains it.

Appearance of a concentrated solution of CuSO _{4 •} 5H ₂ O. Author: PublicDomainPictures. Source: Pixabay.

The resulting mixture is filtered to remove the solid Fe (OH) ₃ and the remaining liquid is treated with ethanol (C ₂ H ₅ OH), methanol (CH ₃ OH) or sulfuric acid to precipitate all the Cu ²⁺ ions as of CuSO _{4 •} 5H ₂ O.

When for example ethanol is added there is less water available so that the ions Cu ²⁺ and SO ₄ ^2- are in solution and tend to bind to each other. It acts as a dehydrator. The more ethanol you add, the more solid it forms.

The precipitated solid can be recrystallized for purification. To do this, it is dissolved in water at a temperature of 80-90 ° C and then the solution is cooled to 25-30 ° C. The pentahydrate compound re-precipitates and the impurities remain in solution.

Applications

It has a wide range of commercial applications.

In agriculture it serves as a pesticide, insecticide, herbicide, fungicide, germicide and soil additive. In veterinary therapies it is used as an anthelmintic, fungicide and emetic (to cause vomiting).

It is used as a blue or green pigment in dyes and colorants, as a mordant in the coloring of fabrics and metals. Also as a photo printing toner and as a reagent to intensify negatives.

It is used in mining activities as a flotation reagent for the recovery of zinc and lead. It is used to produce other copper compounds, it is used in leather tanning and to preserve wood.

In animal feed

This compound is used in the diet of pigs in very small amounts as a growth promoter, especially in the post-weaning phase. The mechanism by which it has this effect is still unknown.

Some researchers claim that it reduces the population of pathogenic or harmful bacteria in the intestines of animals and consequently favors their growth.

With CuSO _{4 •} 5H ₂ O, the development of weaned piglets can be promoted. Author: MabelAmber. Source: Pixabay.

Other scholars indicate that it improves the health of the intestines of these animals, but some research indicates that the intravenous injection of copper also improves their growth.

It has also been used for the same purpose in poultry, and has been used in copper deficiency in ruminants.

In the synthesis of nanoparticles

Copper sulfate pentahydrate has been used to obtain mixed nanoparticles of copper and copper (I) oxide (Cu / Cu ₂ O).

Nanoparticles are extremely small structures that can be seen only through an electron microscope.

Cu / Cu ₂ O powder in nanoparticulate form is used in catalysis or acceleration of chemical reactions, in semiconductors and in antimicrobial materials, among other applications.

In studies for pest control

CuSO _{4 •} 5H ₂ O has been used in experiments to evaluate its toxicity towards snails of the Pomacea canaliculata species.

These are mollusks native to the tropical regions of South America that inhabit various types of ecosystems, from swamps and lagoons to lakes and rivers.

They are studied because some host human parasites such as Schistosoma mansoni (trematode that causes bilharzia disease). Snails can also be harmful to agricultural crops in flooded regions.

Shells of the snails Pomacea canaliculata. H. Zell / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

Eggs deposited by snails on an aquatic plant. These snails are sometimes a pest that can be controlled with CuSO _{4 •} 5H ₂ O. Shan Lv, National Institute of Parasitic Diseases / CC BY (https://creativecommons.org/licenses/by/2.5). Source: Wikimedia Commons.

According to the studies reviewed, aqueous solutions of copper sulfate pentahydrate are extremely toxic to these snails, so this compound can be used to eliminate the mollusk from infested areas.

According to certain research, this is because the snail has no need for the copper ion, so just contact with this ion would be enough for the death of the animal to occur.

In electrically conductive fabrics

This compound has been used to obtain textile materials with integrated electricity sensors. This type of fabric is used in electricity storage devices, pressure sensors, photodetectors and light-emitting screens.

To obtain electrically conductive fabrics, a semi-synthetic woven cellulose fiber called "Lyocell" is coated with metallic copper. The coating is carried out in a non-electrolytic way starting from a solution of CuSO4 • 5H2O and other auxiliary chemical compounds.

Lyocell fiber. This type of cloth was used in copper plating tests. Dobrozhinetsky / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.

The fabric obtained in this way can transfer an electrical signal even under deformation or stretching conditions while maintaining high conductivity.

Effects on the environment

As previously explained, CuSO _{4 •} 5H ₂ O, when dissolved in water, generates the copper (II) ion.

Although copper is essential in low concentrations for the cellular activities of living organisms, in high concentrations it can be toxic and even cause death.

Therefore, the presence of said ion in the environment constitutes a risk for animals and plants. In aquatic ecosystems, it can bioaccumulate in living beings and in the food chain, causing damage.

CuSO _{4 •} 5H ₂ O can be harmful to aquatic environments. Author: JamesDeMers. Source: Pixabay.

In fact, in certain experiences it has been found that the contamination of aquatic environments with copper sulfate pentahydrate causes the biomass of certain aquatic plants to decrease.

Which means that plants grow less in the presence of this salt in high concentrations.

References

1. Lide, DR (editor) (2003). CRC Handbook of Chemistry and Physics. 85 ^th CRC Press.
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3. Alves de Azevedo B., JP and Peixoto, MN (2015). Biomass reduction of Salvinia molesta exposed to copper sulfate pentahydrate (CuSO ₄.5H ₂ O). Rev. Ambient. Water 2015; 10 (3): 520-529. Recovered from doaj.org.
4. Root, W. et al. (2019). Flexible Textile Strain Sensor Based on Copper-Coated Lyocell Type Cellulose Fabric. Polymers 2019, 11, 784. Recovered from mdpi.com.
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