Copper(II) sulfate

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Copper(II) sulfate
Copper(II) sulfate pentahydrate.jpg
Copper(II) sulfate pentahydrate crystal
Names
IUPAC name
Copper(II) sulfate
Other names
Blue vitriol (pentahydrate)
Bluestone (pentahydrate)
Bonattite (trihydrate mineral)
Boothite (heptahydrate mineral)
Chalcanthite (pentahydrate mineral)
Chalcocyanite (mineral)
Cupric sulfate
Properties
CuSO4 (anhydrous)
CuSO4·5H2O (pentahydrate)
Molar mass 159.609 g/mol (anhydrous)
249.685 g/mol (pentahydrate)
Appearance White solid (anhydrous)
Blue solid (pentahydrate)
Odor Odorless
Density 3.60 g/cm3 (anhydrous)
2.286 g/cm3 (pentahydrate)
Melting point anhydrous
650 °C (1,202 °F; 923 K) (decomposition)
pentahydrate
110 °C (230 °F; 383 K) (decomposition)
Boiling point Decomposes
anhydrous
14.3 g/100 ml (0 °C)
17.2 g/100 ml (10 °C)
20.5 g/100 ml (20 °C)
22.3 g/100 ml (25 °C)
24.4 g/100 ml (30 °C)
28.7 g/100 ml (40 °C)
33.7 g/100 ml (50 °C)
39.5 g/100 ml (60 °C)
55.5 g/100 ml (80 °C)
75.4 g/100 ml (100 °C)
pentahydrate
23.1 g/100 ml (0 °C)
27.5 g/100 ml (10 °C)
32 g/100 ml (20 °C)
37.8 g/100 ml (30 °C)
44.6 g/100 ml (40 °C)
61.8 g/100 ml (60 °C)
83.8 g/100 ml (80 °C)
114 g/100 ml (100 °C)
Solubility Anhydrous
Insoluble in ethanol
Pentahydrate
Insoluble in acetone, ethanol
Solubility in methanol pentahydrate
1.04 g/100 ml (18 °C)
Vapor pressure ~0 mmHg
Thermochemistry
5 J ·mol−1·K−1
−769.98 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (anhydrous)
Sigma-Aldrich (pentahydrate)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
300 mg/kg (rat, oral)
Related compounds
Related compounds
 Copper(I) sulfate
Zinc sulfate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Copper(II) sulfate, also known as cupric sulfate, copper sulphate or archaically blue vitriol or vitriol of Cyprus, is the chemical compound with the chemical 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 (CuSO4·5H2O), the most commonly encountered salt, is bright blue and forms triclinic crystals. Copper(II) sulfate exothermically dissolves in water to give the aquo complex [Cu(H2O)6]2+, which has octahedral molecular geometry and is paramagnetic. Copper sulfate pentahydrate occurs in nature as mineral chalcantite.

Properties

Physical properties

Copper(II) sulfate is a blue crystalline solid as the pentahydrate, as it is most commonly seen, and the anhydrous form is a white to light gray powder. It has a solubility of 31.6 g/100 mL at 0˚C and 203.3 g/100 mL at 100˚C. Dissolution is slow yet exothermic, and solutions of copper(II) sulfate are dark blue.

Chemical properties

Copper(II) sulfate is most commonly encountered as the blue pentahydrate, but it can be dehydrated at 200˚C to form the white, powdery, anhydrous variant. At 650˚C, it will decompose to form copper(II) oxide and sulfur trioxide. It emits an emerald green color in a flame test. The copper(II) ions in solution can complex with ammonia to form tetraamminecopper(II) sulfate, which may be crystallized. Copper sulfate dissolves in concentrated hydrochloric acid to form a bright green solution of tetrachlorocupric acid. This color turns to blue when diluted.

Metals more reactive than copper will react with copper(II) sulfate, leaving the sulfate salt of the metal and copper. Example, using zinc metal:

CuSO4 + Zn → ZnSO4 + Cu

The solid obtained can be treated with hydrochloric acid to get rid of excess zinc and other impurities.

Availability

Copper(II) sulfate can be found at most hardware stores as root killer for use in septic systems. These products are usually fairly pure, but require recrystallization to ensure their purity. This source, however, is suitable for use in crystal growing. It can be made from copper metal, nitric acid or hydrogen peroxide, and concentrated sulfuric acid, but this method is economically impractical if not used on an industrial scale.

Preparation

Copper(II) sulfate can also be produced by the electrolysis of sulfuric acid with a copper anode and cathode. The cathode needs to be shielded at the top and exposed at the bottom of the solution. The anode should reside at the very top. The copper(II) sulfate will form a beautiful dark blue layer at the bottom. The solution should be decanted and crystallized.

A simpler route involves reacting copper "rust", like oxide, hydroxide or carbonate with sulfuric acid. Keep adding copper oxide until all the acid has been consumed, filter the solution then recrystallize the compound from the solution.

Likewise, bubbling sulfur dioxide in an aqueous suspension of copper oxide or copper hydroxide will give copper sulfite, which will oxidize in air to copper sulfate.

Projects

Handling

Safety

All copper salts, especially soluble ones, are moderately toxic. They should be stored out of reach of small children and pets. They are also toxic to the environment.

Storage

Copper sulfate hydrated can be stored in closed bottles. Anhydrous variety must be stored in sealed closed containers to prevent it from absorbing water from air.

Disposal

Copper sulfate can be disposed of by either precipitating it as the copper(II) carbonate, which is insoluble, and disposing of it as toxic waste.

Another good way is to reduce it with iron or zinc to elemental copper, that can be reused, while the resulting iron or zinc sulfate are much easier to dispose of, as they're less hazardous to the environment.

Gallery

  • Shielded copper cathode

  • Electrolytic cell for producing copper(II) sulfate

  • Copper(II) sulfate product, electrolytically produced

  • Anhydrous copper sulfate

  • Crystal showing the structure of the pentahydrate

  • Copper sulfate crystals made by the hydrogen peroxide/sulfuric acid method

  • A boiling solution of copper(II) sulfate prior to recrystallization

See also

References

Relevant Sciencemadness threads

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