Copper(II) sulfate

Chemical properties

Copper(II) sulfate pentahydrate decomposes before melting. It loses two water molecules upon heating at 63 °C (145 °F), followed by two more at 109 °C (228 °F) and the final water molecule at 200 °C (392 °F).

The chemistry of aqueous copper sulfate is simply that of copper aquo complex, since the sulfate is not bound to copper in such solutions. Thus, such solutions react with concentrated hydrochloric acid to give tetrachlorocuprate(II):

Cu²⁺ + 4 Cl⁻ → CuCl₄²⁻

Similarly treatment of such solutions with zinc gives metallic copper, as described by this simplified equation:

CuSO₄ + Zn → Cu + ZnSO₄

A further illustration of such single metal replacement reactions occurs when a piece of iron is submerged in a solution of copper sulfate:

Fe + CuSO₄ → FeSO₄ + Cu

In high school and general chemistry education, copper sulfate is used as an electrolyte for galvanic cells, usually as a cathode solution. For example, in a zinc/copper cell, copper ion in copper sulfate solution absorbs electron from zinc and forms metallic copper.

Cu²⁺ + 2 e⁻ → Cu (cathode), E^°_cell = 0.34 V

Copper sulfate is commonly included in teenage chemistry sets and undergraduate experiments. It is often used to grow crystals in schools and in Copper electroplating experiments despite its toxicity. Copper sulfate is often used to demonstrate an exothermic reaction, in which steel wool or magnesium ribbon is placed in an aqueous solution of CuSO₄. It is used to demonstrate the principle of mineral hydration. The pentahydrate form, which is blue, is heated, turning the copper sulfate into the anhydrous form which is white, while the water that was present in the pentahydrate form evaporates. When water is then added to the anhydrous compound, it turns back into the pentahydrate form, regaining its blue color. Copper(II) sulfate pentahydrate can easily be produced by crystallization from solution as copper(II) sulfate, which is hygroscopic.

Uses

As a fungicide and herbicide

Copper sulfate has been used for control of algae in lakes and related fresh waters subject to eutrophication. It "remains the most effective algicidal treatment".

Bordeaux mixture, a suspension of copper(II) sulfate (CuSO₄) and calcium hydroxide (Ca(OH)₂), is used to control fungus on grapes, melons, and other berries. It is produced by mixing a water solution of copper sulfate and a suspension of slaked lime.

A dilute solution of copper sulfate is used to treat aquarium fishes for parasitic infections, and is also used to remove snails from aquariums and zebra mussels from water pipes. Copper ions are highly toxic to fish. Most species of algae can be controlled with very low concentrations of copper sulfate.

Analytical reagent

Several chemical tests utilize copper sulfate. It is used in Fehling's solution and Benedict's solution to test for reducing sugars, which reduce the soluble blue copper(II) sulfate to insoluble red copper(I) oxide. Copper(II) sulfate is also used in the Biuret reagent to test for proteins.

Copper sulfate is used to test blood for anemia. The blood is dropped into a solution of copper sulfate of known specific gravity—blood with sufficient hemoglobin sinks rapidly due to its density, whereas blood which sinks slowly or not at all has an insufficient amount of hemoglobin. Clinically relevant, however, modern laboratories utilize automated blood analyzers for accurate quantitative hemoglobin determinations, as opposed to older qualitative means.

In a flame test, the copper ions of copper sulfate emit a deep green light, a much deeper green than the flame test for barium.

Organic synthesis

Copper sulfate is employed at a limited level in organic synthesis. The anhydrous salt is used as a dehydrating agent for forming and manipulating acetal groups. The hydrated salt can be intimately mingled with potassium permanganate to give an oxidant for the conversion of primary alcohols.

Rayon production

Reaction with ammonium hydroxide can yield tetraamminecopper(II) sulfate and Schweizer's reagent (nonsulphurous), which is used to dissolve cellulose in the industrial production of Rayon.

Niche uses

Copper(II) sulfate has attracted many niche applications over the centuries. In industry copper sulfate has multiple applications. In printing it is an additive to book-binding pastes and glues to protect paper from insect bites; in building it is used as an additive to concrete to improve water resistance and prevent plant and mushroom growth. Copper sulfate can be used as a coloring ingredient in artworks, especially glasses and potteries. Copper sulfate is also rarely used in firework manufacture as a blue coloring agent, but it is not safe to mix copper(II) sulfate with metal powders, or it or any copper(II) compound with chlorates; the sulfate and other copper(II) compounds are not allowed in chlorate containing mixtures in the US.

Copper sulfate was once used to kill bromeliads, which serve as mosquito breeding sites. Copper sulfate is used as a molluscicide to treat bilharzia in tropical countries.

Art

In 2008, the artist Roger Hiorns filled an abandoned waterproofed council flat in London with 75,000 liters of copper(II) sulfate water solution. The solution was left to crystallize for several weeks before the flat was drained, leaving crystal-covered walls, floors and ceilings. The work is titled Seizure. Since 2011, it has been on exhibition at the Yorkshire Sculpture Park.

Etching

Copper(II) sulfate is used to etch zinc, aluminium, or copper plates for intaglio printmaking. It is also used to etch designs into copper for jewelry, such as for Champlevé.

Dyeing

Copper(II) sulfate can be used as a mordant in vegetable dyeing. It often highlights the green tints of the specific dyes.

Electronics

An aqueous solution of copper(II) sulfate is often used as the resistive element in liquid resistors.

In electronic and microelectronic industry a bath of CuSO₄·5H₂O and sulfuric acid (H₂SO₄) is often used for electrodeposition of copper.

Other forms of copper sulfate

Anhydrous copper(II) sulfate can be produced by dehydration of the commonly available pentahydrate copper sulfate. In nature, it is found as the very rare mineral known as chalcocyanite. The pentahydrate also occurs in nature as chalcanthite. Other rare copper sulfate minerals include bonattite (trihydrate), boothite (heptahydrate), and the monohydrate compound poitevinite. There are numerous other, more complex, copper(II) sulfate minerals known, with environmentally important basic copper(II) sulfates like langite and posnjakite.

Forms of copper(II) sulfate

Toxicological effects

Copper(II) salts have an LD50 of 100 mg/kg.

Copper(II) sulfate was used in the past as an emetic. It is now considered too toxic for this use. It is still listed as an antidote in the World Health Organization's Anatomical Therapeutic Chemical Classification System.