|
(1) Halides of copper : Copper (II) chloride,
CuCl2 is prepared by passing chlorine over heated copper. Concentrated aqueous solution of
CuCl2 is dark brown but changes first to green and then to blue on dilution.
On heating, it disproportionates to copper (I) chloride and chlorine
It is used as a catalyst in the Daecon’s process for the manufacture of chlorine.
Copper (I) chloride,
CuCl is a white solid insoluble in water. It is obtained by boiling a solution of CuCl2
withexcess of copper turnings and conc.
HCl.
HCl
CuCl2 + Cu ————→ 2CuCl
It dissolves in conc. HCl
due to the formation of complex H[CuCl2]
CuCl + HCl ————→ H [CuCl2]
It is used as a catalyst alongwith
NH4Cl in the preparation of synthetic rubber.
(2) 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.
(3) 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 ————→ 2CuO + 4NO2 + O2
(4) 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.
503K
CuSO4.5H2O ————→ CuSO4 + 5H2O
Blue White
At about 1000 K, CuSO4
decomposes to give
CuO and
SO3.
1000K
CuSO4————→CuO + SO3
(ii) It gives a deep blue solution of tetrammine copper (II) sulphate with
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]
(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. Like Verdigris which is
Cu(CH3COO)2Cu(OH)2 i.e. basic copper acetate and is used as a green pigment in paints. As a fungicide in starch paste for book binding work.
(5) Cupric sulphide
CuS It is prepared as follows :
Cu(NO3)2 + H2S → CuS + 2HNO3.
Black ppt.
(6) Basic copper carbonates : Because of lower solubility of the hydroxide, the normal carbonate does not exist. Two basic copper carbonates occur in nature viz malachite CuCO3.Cu(OH)2
which has a fine green colour, and azurite, 2CuCO3, Cu(OH)2
which is deep blue in colour.
Malachite is prepared by heating a mixture of CuSO4
solution and limestone in a sealed tube at 423 – 443 K. 423-443 K
2CuSO4 + 2CaCO3 + H2O —————→ CuCO3Cu(OH)2 + 2CaSO4 + CO2
Malachite
At lower temperature azurite is formed
< 423
3CuSO4 + 3CaCO3 + H2O —————→ 2CuCO3Cu(OH)2 + 3CaSO4 + CO2
Azurite
On heating, both decompose to give black cupric oxide, water and
CO2.
They are used as green and blue painter’s pigments under the name ‘malachite green’ and azurite blue’.
|
Home