Copper(II) sulfate, also known as cupric sulfate or simply copper sulphate, 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 gray-white powder or sometimes pale green, 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(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/100mL at 0˚C and 203.3 g/100mL at 100˚C. Dissolution is slow yet exothermic, and solutions of copper(II) sulfate are dark blue.
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.
- CuSO4 + Zn → ZnSO4 + Cu
The solid obtained can be treated with hydrochloric acid to get rid of excess zinc and other impurities.
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.
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.
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.
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.
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.
- CRC Handbook of Chemistry and Physics 66th Edition (1985-1986)
- Personal electrolytic manufacture by Arkoma29