Copper sulfate (CuSO₄)

Copper sulfate may refer to either cuprous sulfate (Cu₂SO₄) or cupric sulfate (CuSO₄). However, the term most commonly refers to cupric sulfate. The systematic name for CuSO₄ is copper(II) sulfate, though it is also known by several other names such as blue vitriol, Roman vitriol, vitriol of copper, and bluestone.

The most frequently encountered copper(II) sulfate form is its pentahydrate, with the chemical formula CuSO₄·5H₂O. This form is easily recognized by its vivid blue color. In contrast, the anhydrous form of the salt is a white powder.

The CuSO₄ molecule features an ionic bond between a copper ion (Cu²⁺) and a sulfate ion (SO₄²⁻). The oxidation state of copper in this compound is +2.

Copper sulfate can be synthesized either by reacting metallic copper with hot, concentrated sulfuric acid, or by reacting copper oxides with dilute sulfuric acid.

1.0Manufacturing of Copper Sulfate

The production of copper sulfate often begins with virgin copper as the primary raw material. However, non-ferrous scrap metal is also a significant source. This scrap is first purified, then melted and poured into water, forming rough, spherical, porous particles similar in size to marbles—commonly referred to as copper shot.

These copper shots are then dissolved in dilute sulfuric acid in the presence of air, producing a hot, saturated solution (or liquor) of copper sulfate.

To form crystals, the solution is allowed to cool. For the production of large, traditional crystals, the solution is cooled slowly in large cooling vats. Lead strips placed in the vats act as a surface on which the crystals can grow.

If granular or snow-like crystals are desired, the cooling is accelerated using water-cooled vessels, resulting in a finer crystalline product.

2.0Physical Properties of Copper Sulfate

• The molar mass of anhydrous copper sulfate (CuSO₄) is 159.609 g/mol, while the pentahydrate form (CuSO₄·5H₂O) has a molar mass of 249.685 g/mol.
• Anhydrous CuSO₄ is a gray-white powder, whereas the pentahydrate form is known for its bright blue appearance.
• The density of anhydrous copper sulfate is approximately 3.6 g/cm³, while the pentahydrate form has a lower density of around 2.286 g/cm³.
• Both forms decompose upon heating, which means they do not have a well-defined boiling point.
• The crystal structure of CuSO₄·5H₂O is orthorhombic, whereas anhydrous CuSO₄ forms triclinic crystals.

3.0Chemical Properties of Copper Sulfate

• Copper(II) ions (Cu²⁺) in copper sulfate react with chloride ions (Cl⁻) from concentrated hydrochloric acid, forming a complex ion known as tetrachlorocuprate(II). The reaction is represented as:

${\text{Cu}}^{2+}+4{\text{Cl}}^{-}\to {\text{CuCl}}_4^{2-}Cu2++4Cl-\to CuCl42-$

• When copper sulfate (CuSO₄) is heated to around 650°C, it decomposes to form cupric oxide (CuO) and sulfur trioxide (SO₃):

${\text{CuSO}}_4\stackrel{heat}{\to }\text{CuO}+{\text{SO}}_3$

• Copper sulfate is highly soluble in water, with its solubility increasing with temperature. At 10°C, the solubility is approximately 1.055 molal, and at 30°C, it increases to 1.502 molal.
• A classic example of a single displacement reaction is the reaction between iron (Fe) and copper sulfate (CuSO₄), where iron displaces copper from the solution. The balanced chemical equation is:

$\text{Fe}+{\text{CuSO}}_4\to {\text{FeSO}}_4+\text{Cu}$

4.0Uses of Copper Sulfate

• The pentahydrate form of copper sulfate (CuSO₄·5H₂O) is widely used as a fungicide due to its ability to kill a broad range of fungi.
• It serves as a key ingredient in Benedict’s solution and Fehling’s solution, both of which are used to perform tests for reducing sugars.
• Copper sulfate is also used in medical diagnostics, such as testing blood samples for conditions like anemia.
• In the vegetable dyeing process, it acts as a mordant (dye fixative) to help bind dyes to fabrics more effectively.
• Aqueous solutions of copper sulfate are used in liquid resistors as resistive elements in certain electrical applications.
• It finds application in decorative work, as it can impart color to cement, ceramics, and various metals, making it useful in art and construction.
• Additionally, copper sulfate is added to bookbinding adhesives to repel insects and protect printed materials from pest damage.

5.0Industrial Applications of Copper Sulfate

• Copper plating: Copper sulfate is used as an essential component in the electroplating process to deposit a layer of copper on metal surfaces.
• Mining industry: It acts as an activator in the froth flotation process, helping in the extraction and concentration of lead, gold, and cobalt ores.
• Printing and engraving: Copper sulfate serves as an electrolyte in the production of electrotypes and is used as an etching agent for engraving metal plates in printmaking.
• Glass and ceramics: It is used to color glass and in various ceramic applications.
• Marine coatings: Copper sulfate is a key ingredient in anti-fouling paints that prevent the growth of marine organisms on ships and underwater structures.
• Due to its wide range of properties, copper sulfate is utilized across numerous industries, making it a highly versatile industrial chemical.