Copper(II) sulfate 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. The anhydrous form occurs as a rare mineral known as chalcocyanite. The hydrated copper sulfate occurs in nature as
chalcanthite (pentahydrate), and two more rare ones: bonattite (trihydrate) and boothite (heptahydrate). Archaic names for copper(II) sulfate are "blue vitriol" and "bluestone".
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; this oxide can be generated with the addition of hydrogen peroxide to the acid. It may also be prepared by electrolyzing sulfuric acid, using copper electrodes.
Chemical properties
Copper(II) sulfate pentahydrate
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 (SO
3). When heated in an open flame the crystals are dehydrated and turn grayish-white.
Uses
As an herbicide, fungicide, pesticide
Copper sulfate pentahydrate is a
fungicide. Mixed with
lime it is called
Bordeaux mixture and used to control fungus on grapes, melons, and other berries. Another application is
Cheshunt compound, a mixture of copper sulfate 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 for various parasitic infections, 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.
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 also used to test blood for anemia. The blood is tested by dropping it into a solution of copper sulfate of known specific gravity — blood which contains sufficient hemoglobin sinks rapidly due to its density, whereas blood which does not, floats or sinks slowly.
In a flame test, its copper ions emit a deep blue-green light, much more blue than the flame test for barium.
Organic synthesis
Copper sulfate is employed in
organic synthesis. The anhydrous salt catalyses the trans
acetalization in organic synthesis. The hydrated salt reacts with
potassium permanganate to give an oxidant for the conversion of primary alcohols.
Chemistry education
Copper sulfate is a commonly included chemical in children's
chemistry sets and is often used to grow crystals in
schools and in
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 CuSO
4. 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 color, and is known as blue copperas.
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.
- Fe + CuSO4 → FeSO4 + Cu
The copper can also be electroplated to the iron.
Other uses
Other applications include hair
dyes, coloring glass, processing of
leather and
textiles and in pyrotechnics as a green colorant. It is used by some organic cattle farmers in solution as a footbath as a way of increasing the hardness of hoof, thereby reducing incidence of lameness. It also can change the color of a flame if added to it in its dry state, making it green.
References
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