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  Inorganic Chemistry >> S and P Block Elements >
Copper Ores and its Extraction :
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(1) Ores : Copper pyrites (chalcopyrite) CeFeS2 Cuprite (ruby copper) Cu2O Copper glance (Cu2S), Malachite [Cu(OH)2.CuCO3] Azurite [Cu(OH)2.2CuCO3]

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

Concentration of ore : Froth floatation process.

Roasting: Main reaction:

2CuFeS2 + O2 → Cu2S + 2FeS + SO2.

Side reaction:

2Cu2S + 3O2 → 2Cu2O + 2SO2

2FeS + 3O2 → 2FeO + 2SO2.

Smelting:

FeO + SiO2 → FeSiO3 (slag)

Cu2O + FeS → FeO + Cu2S

The mixture of copper and iron sulphides melt together to form 'matte' (Cu2S + FeS) 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). Slag is removed. By this time most of iron sulphide is removed.

Cu2S + 2Cu2O → 6Cu + SO2

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. Copper is second most useful metal (first being iron). It undergoes displacement reactions with lesser reactive metals e.g. with Ag. It can displace Ag from AgNO3. The finally divided Ag so obtained is black in colour.

Copper shows oxidation states of +1 and +2. Whereas copper (I) salts are colourless, copper (II) salts are blue in colour. Cu (I) salts are less stable and hence are easily oxidised to Cu (II) salts (2Cu+ → Cu2+ + Cu) . This reaction is called disproportionation.

(1) In presence of atmospheric CO2 and moisture, copper gets covered with a green layer of basic copper carbonate (green layer) which protects the rest of the metal from further acton.

Cu + O2 + CO2 + H2O → Cu(OH)2 CuCO3
                                                   green layer

(2) In presence of oxygen or air, copper when heated to redness (below 1370K) first forms red cuprous oxide which changes to black cupric oxide on further heating. If the temperature is too high, cupric oxide changes back to cuprous oxide

                         Below 1370K                                                       O2

4Cu + O2 ————————→ 2Cu2O ————————→ 4CuO
                                                              (Red)      Above 1370K (Black)

                                    High temp
CuO + Cu ————————→ Cu2O

(3) Action of acids. Non oxidising dil. acids such as HCl, H2SO4 have no action on copper. However, copper dissolves in these acids in presence of air.

Cu + 2HCl + 1/2 O2(air) → CuCl2 + H2O

With dil. HNO3, Cu liberates NO (nitric oxide)

3Cu + 8HNO3 →, copper gives NO2

Cu + 4HNO3 → 3Cu(NO3)2 + 2NO2 + 2H2O

With hot conc. H2SO4, copper gives SO2

Cu + 2H2SO4 → CuSO4 + SO2 + 2H2O

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  Inorganic Chemistry >> S and P Block Elements >
Manganese Containing Compounds :
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Potassium Permanganate, (KMnO4)

Potassium permanganate is a salt of an unstable acid HMnO4 (permanganic acid). The Mn is an +7 state in this compound.

Preparation : Potassium permanganate is obtained from pyrolusite as follows.

Conversion of pyrolusite to potassium manganate : When manganese dioxide is fused with potassium hydroxide in the presence of air or an oxidising agent such as potassium nitrate or chlorate, potassium manganate is formed, possibly via potassium manganite.

MnO2 + 2KOH ––––––→ K2MnO3 + 4H2O] × 2
                                                  potassium manganite
2K2MnO3 + O2 ––––––→ 2K2MnO4 + 2H2O
                                                  fused
2MnO2 + 4KOH + O2 ––––––→ 2K2MnO4 + 2H2O
pyrolusite                                              potassium manganate
                                                             [dark-green mass]
Oxidation of potassium manganate to potassium permanganate: The potassium manganate so obtained is oxidized to potassium permanganate by either of the following methods.

By chemical method : The fused dark-green mass is extracted with a small quantity of water. The filtrate is warmed and treated with a current of ozone, chlorine or carbon dioxide. Potassium manganate gets oxidized to potassium permanganate and the hydrated manganese dioxide precipitates out. The reactions taking place are,

When CO2 is passed

3K2MnO4 + 2H2O → 2KMnO4 + MnO2 ↓ + 4KOH
potassium manganate         potassium permanganate

2CO2 + 4KOH → 2K2CO3 + 2H2O

When chlorine or ozone is passed

2K2MnO4 + Cl2 → 2KMnO4 + 2KCl

2K2MnO4 + O3 + H2O → 2KMnO4 + 2KOH + O2(g)
The purple solution so obtained is concentrated and dark purple, needle-like crystals having metallic lustre are obtained.

Electrolytic method : Presently, potassium manganate (K2MnO4) is oxidized electrolytically. The electrode reactions are,

At anode: 2MnO42– → 2MnO4– + 2e–

At cathode: 2H+ + 2e– → H2(g)

The purple solution containing KMnO4 is evaporated under controlled condition to get crystalline sample of potassium permanganate.

Physical properties

KMnO4 crystallizes as dark purple crystals with greenish luster (m.p. 523 K).

It is soluble in water to an extent of 6.5g per 100g at room temperature. The aqueous solution of KMnO4 has a purple colour.

 

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