What Is Copper Hydroxide?
Copper hydroxide is the hydroxide of copper and is a pale blue amorphous powdery solid.
Copper ions have two valences, monovalent (Cu+) and divalent (Cu2+). Copper hydroxide generally refers to Cu (OH)2, which is divalent copper (II) hydroxide.
Uses of Copper Hydroxide
Copper hydroxide (II) is mainly used in the manufacture of processed cellulose-based products such as rayon and cellophane, in the manufacture of other copper salts, as a mordant, pigment, disinfectant, and insecticide.
1. Cellulose Raw Material Products
Since cellulose is insoluble in most solvents and is itself difficult to melt, it is denatured to a solvent-soluble state by chemical treatment and then processed into fibrous or film-like forms. Copper Hydroxide is used in this chemical treatment.
Dissolving copper hydroxide in an aqueous ammonia solution produces a tetra ammonium copper complex, yielding a deep blue solution known as Schweitzer’s reagent.
Synthesis of Schweitzer reagent:
Cu(OH)2 + 4NH4OH → [Cu(NH3)4(H2O)2](OH)2 + 2H2O
Schweitzer’s reagent neutralizes the hydroxyl group of cellulose with its own hydroxide ion (OH-). Copper ions (Cu2+) coordinate to the neutralized hydroxyl groups of cellulose to form complex ions, which dissolve cellulose.
Complex formation between cellulose and copper:
2(C6H10O5)n + n[Cu(NH3)4(H2O)2](OH)2 → n(C6H10O5)2[Cu(NH3)4(H2O)2] + 2nH2O
After the cellulose dissolved in Schweitzer’s reagent has undergone the necessary treatment, Cu2+ is desorbed from the hydroxyl group complex ionized by dilute sulfuric acid or other means and re-deposited back to H to be recovered as a cellulose product such as rayon.
Regeneration of cellulose:
n(C6H10O5)2[Cu(NH3)4(H2O)2] + 3nH2SO4 → 2(C6H10O5)n + nCuSO4 + 2n(NH4)2SO4
2. Fungicides and Insecticides
Copper ions have an excellent preventive effect against bacterial as well as filamentous fungus-derived diseases. Therefore, it can be used as a pesticide for a wide range of citrus plants, other fruits, and vegetables. However, it may cause chemical damage and must be used in combination with calcium carbonate hydrate when used.
Characteristics of Copper Hydroxide
Copper hydroxide is a pale blue solid with a molecular weight of 97.56, specific gravity of 2.368, and a melting point of 60~80℃. It is insoluble in cold water and dilute acid, but decomposes to CuO in hot water. It is soluble in ammonia water and alkali cyanide solution, forming complex salts.
It is also soluble in alkaline hydroxide solutions, producing a purple colloidal solution. When heated near its melting point, it becomes CuO and turns black. Although highly stable at room temperature and pressure, it is hazardous to the aquatic environment both in the short and long term, so care should be taken when disposing of it.
CuOH, a monovalent copper (I) hydroxide, is a yellow precipitate formed when alkali hydroxide is added to an aqueous copper (I) salt solution (e.g., CuCl), and is said to be a precipitate of copper oxide Cu2O.
Other Information on Copper Hydroxide
Production Method of Copper Hydroxide
Copper hydroxide is formed by adding sodium hydroxide to an aqueous solution of copper (II) sulfate, resulting in the formation of a blue precipitate. This is then dehydrated to obtain a blue powder of copper hydroxide.
Main reaction: CuCl2 + 2NaOH → Cu(OH)2 + 2NaCl