d Block Elements : Copper and its Compounds

Copper and its Compounds

Ores : Copper pyrites (chalcopyrite) CuFeS2. Cuprite (ruby copper) Cu2O, Copper glance (Cu2S), Malachite [Cu(OH)2. CuCO3, Azurite [Cu(OH)2. 2CuCO3]

Extraction : Most of copper (about 75%) is extracted from its sulphide ore, copper pyrites.

Concentration of ore : by Froth floatation process.

Roasting :

Main reactions :  2CuFeS2 + O2 → Cu2S + 2FeS + SO2.

Side reaction : 2Cu2S + 3O2 → 2Cu2O + 2SO2;

2FeS + 3O2 → 2FeO + 2SO2.

Smelting : FeO + SiO2 → FeSiO3 (slag); Cu2O + FeS → FeO + Cu2S

Note :   The mixture of copper and iron sulphides melt together to form ‘matte’ and the slag floats on its surface.

Conversion of matte into Blister copper (Bessemerisation) : Silica is added to matte and a hot blast of air is passed FeO + SiO2 → FeSiO3 Slag is removed. By this time most of iron sulphide is removed. 

Cu2S + 2Cu2O → 6Cu + SO2

Note :    Blister copper : Which contain about 98% pure copper and 2% impurities (Ag, Au, Ni, Zn etc.)

Properties of copper : It has reddish brown colour. It is highly malleable and ductile. It has high electrical conductivity and high thermal conductivity. In presence of CO2 and moisture Cu is covered with a green layer of CuCO3. Cu(OH)22Cu + H2O + CO2 + O2 → CuCO3. Cu(OH)2. It undergoes displacement reactions with lesser reactive metals e.g. with Ag. It can displace Ag from. The finally divided Ag so obtained is black in colour.

 

Compounds of copper

Cuprous oxide Cu2O : It is a reddish brown powder insoluble in water but soluble in ammonia solution, where it forms diammine copper (I) ion. Cu+ + 2NH3 → [Cu(NH3)2]+. It is used to impart red colour to glass in glass industry. 

Cupric oxide CuO : It is dark black, hygroscopic powder which is reduced to Cu by hydrogen, CO etc. It is used to impart light blue colour to glass. It is prepared by heating copper nitrate.

                   2Cu (NO3)2  \underrightarrow { \quad \Delta \quad } 2CuO + 4NO2 + O2

Copper sulphate CuSO4. 5H2O (Blue vitriol) : It is prepared by action  of dil H2SO4 on copper scrap in presence of air. 

2Cu + 2H2SO4 + O2 → CuSO4 + 2H2O

                             air

(i)      On heating this blue salt becomes white due to loss of water of crystallization.

                   CuSO4. 5H2O  \underrightarrow { \quad 503\quad K\quad } CuSO4 + 5H2O

                             Blue                    White

At about 1000 K, CuSO4 decomposes to give CuO and SO3.

                   CuSO4  \underrightarrow { \quad 1000\quad K\quad } CuO + SO3

(ii)     It gives a deep blue solution of tetrammine copper (II) sulphate with NH4OH.

                   Cu2SO4 + 4NH4OH. → [Cu(NH3)4]SO4 + 4H2O

                                                                   Blue colour

(iii)    With KCN it first gives yellow precipitate of CuCN which decomposes of give Cu2(CN)2. Cu2(CN)2 dissolves in excess of KCN to give K3 [Cu(CN)4]

                   2CuSO4 + 4KCN → Cu2 (CN)2 + 2K2SO4 + (CN)2

(iv)    With KI it gives white ppt. of Cu2I2

                   4KI + 2CuSO4 → 2K2SO4 + Cu2I2 + I2

                                                                   White ppt.

(v)     With K4[Fe(CN)6], CuSO4 gives a reddish brown ppt. of Cu2[Fe(CN)6]

                   2CuSO4 + K4[Fe(CN)6] → Cu2[Fe(CN)6] + 2K2SO4

                                                                   Reddish brown ppt.

 

Uses : For electroplating and electrorefining of copper. As a mordant in dyeing. For making Bordeaux mixture (11 parts lime as milk of lime + 16 parts copper sulphate in 1,000 parts of water). It is an excellent fungicide. For making green pigments containing copper carbonate and other compounds of copper.  As a fungicide in starch paste for book binding work.

Cupric sulphide CuS : It is prepared as follows :

Cu(NO3)2 + H2S → CuS + 2HNO3.

                                      Black ppt.

Cupric chloride CuCl2 : It is a dark brown solid soluble in water and its aqueous solution first changes to green and then to blue on dilution.

Cuprous chloride Cu2Cl2 : It is a white solid insoluble in water and dissolves in conc.  HCl due to formation of H[CuCl2] complex.