Copper(II) sulfate ("sulphate" in most Commonwealth nations) is the
chemical compound with the formula
CuSO4. This salt
exists as a series of compounds that differ in their degree of hydration. The
anhydrous form is a pale green or gray-white powder, whereas the pentahydrate, the most
commonly encountered salt, is bright blue. This hydrated copper sulfate occurs in nature as the mineral called chalcanthite. Archaic names for copper(II) sulfate are
"blue vitriol" and "bluestone"[1]
Structure
In the pentahydrate, copper(II) is bonded to four molecules of water and to the oxygen atoms of two sulfate anions. The fifth
water is not coordinated, but links the sulfate anions via hydrogen bonding. In the
trihydrate, all three water molecules are bonded as well as one oxygen atom of the sulfate, to define a distorted square planar
arrangement, two more oxygen ligands are ca. 2.4 Å distant from copper. In the anhydrous form, copper is bound to four oxygen
atoms of sulfate (rCu-O = 1.9-2.0Å) and more weakly bonded to two other oxygen atoms (2.4 Å).[2] A monohydrate is also known.
Preparation
Since it is available commercially, copper sulfate is usually purchased, not prepared in the laboratory. It can be made by the
action of sulfuric acid on a variety of copper(II) compounds, for example copper(II) oxide. Copper(II) sulfate decomposes before
melting, losing four water molecules at 110 °C and all five at 150 °C. At 650 °C, copper(II) sulfate decomposes into copper(II)
oxide (CuO) and sulfur trioxide (SO3). When heated in an open flame the
crystals are dehydrated and turn grayish-white.[3]
Uses
In organic synthesis
Copper sulfate is employed in organic synthesis.[4] The anhydrous salt catalyses the transacetalization in organic synthesis.[5] The
hydrated salt reacts with potassium permanganate to give an oxidant for the
conversion of primary alcohols.[6]
In school chemistry demonstrations
Copper sulfate is a commonly included chemical in children's chemistry sets and is
often used in high school crystal growing.[7] and copper plating experiments. Due to its toxicity, it is not recommended for small children. 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 in school chemistry courses 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 colour.
Large crystals of copper sulfate
In an illustration of a "single metal replacement reaction," iron is submerged in a solution of copper sulfate. Upon standing,
iron dissolves and copper precipitates.
As an herbicide, fungicide, pesticide
Copper sulfate pentahydrate is a fungicide. Mixed with lime it is called Bordeaux mixture to control fungus on grapes
and other berries[8], another application is Cheshunt compound, a mixture of copper sulphate and ammonium carbonate used in horticulture to prevent
damping off in seedlings. Its use as an herbicide is not agricultural, but instead for control
of invasive exotic aquatic plants and the roots of other invasive plants near various pipes that contain water. A dilute solution
of copper sulfate is used to treat aquarium fish of various parasitic infections[9], and is also used to remove snails from aquariums. However, as the copper ions are also highly toxic
to the fish, care must be taken with the dosage. Most species of algae can be controlled with very low concentrations of copper
sulfate. Copper sulfate inhibits growth of bacteria such as E. coli.
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 also used to test blood for anemia[10]. A drop of the patient's blood is dropped into an aqueous solution of copper
sulfate solution: if it sinks within a certain time, then the patient has sufficient hemoglobin levels and is not anemic. If the blood drop floats or sinks slowly, then the patient is
iron-deficient and may be anemic.
In a flame test, its copper ions emit a deep blue-green
light, much more blue than the flame test for barium.
Other uses
Other applications include hair dyes, coloring glass, processing of leather and textiles, and in pyrotechnics as a green colorant.[11] A full list of uses can be seen here.
Safety
Copper salts are toxic in large amounts.[12]
References
- ^ http://ptcl.chem.ox.ac.uk/MSDS/CO/copper_II_sulfate.html
- ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon
Press. ISBN 0-19-855370-6.
- ^ Holleman, A. F.; Wiberg, E. Inorganic Chemistry Academic Press: San
Diego, 2001. ISBN 0-12-352651-5.
- ^ Hoffman, R. V. "Copper(II) Sulfate" Encyclopedia of Reagents for Organic
Synthesis, 2001 John Wiley & Sons. DOI: 10.1002/047084289X.rc247
- ^ Hulce, M. Mallomo, J. P.; Frye, L. L.; Kogan, T. P.; Posner, G. H. “(S)-( +
)-2-(p-Toluenesulfinyl)-2-Cyclopentanone: Precursor for Enantioselective Synthesis of 3-Substituted Cyclopentanones” Organic
Syntheses, Collected Volume 7, p.495 (1990).
- ^ Jefford, C. W.; Li, Y.; Wang, Y. “A Selective, Heterogeneous Oxidation using
a Mixture of Potassium Permanganate and Cupric Sulfate: (3aS,7aR)-Hexahydro-(3S,6R)-Dimethyl-2(3H)-Benzofuranone” Collective
Volume 9, page 462.
- ^ http://www.newton.dep.anl.gov/askasci/chem03/chem03203.htm
- ^ http://www.copper.org/applications/compounds/copper_sulfate02.html
- ^ http://www.fishdoc.co.uk/treatments/copper.htm
- ^ http://cat.inist.fr/?aModele=afficheN&cpsidt=2686293
- ^ http://www.copper.org/applications/compounds/table_a.html
- ^ http://ptcl.chem.ox.ac.uk/MSDS/CO/copper_II_sulfate.html
External links
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