Occurrence of Metals Chemistry Notes

Occurrence of Metals Chemistry Notes

Occurrence of Metals :

Metals occur in nature in two states :

→ In Free State : These are noble metals which are less active. They do not react with air, oxygen, moisture, CO2 and other elements. For example: Gold, Platinum etc.

→ In Combined State : Most of the metals in nature occur in the combined state due to their reactivity. They react with moisture, oxygen, CO2 (by oxidation or roduction) and form compounds.

→ Minerals : In nature, metals are found in combined state, in which compounds of various metals are mixed and they are associated with large number of earthly, rocky and sand impurities etc. are present. In combined form are known as minerals. The places where they are found are known as mines.

Occurrence of Metals Chemistry Notes

→ Ore : The minerals from which different metals can be economically and conveniently extracted are called ores. “All the ores are minerals but all the minerals are not ores.” In nature, metals are found in the form of oxides. sulphides, sulphates, carbonates, silicates, halides, nitrates, phosphates etc. For example : Due to impure form of Cr in Al2O3 various gemstones are obtained.

  • Ruby : Impurity of Cr in Al2O3.
  • Blue Sapphire : Impurity of Co in Al2O3.

→ Every mineral of the metal cannont be used as ore. To understand the difference between mineral and ore, let us consider an example of aluminium. The earth’s crust contain, two mineral, of aluminium, bauxite (Al2O3 . 2H2O) and China clay (Al2O3 . 2SiO2 . 2H2O) But the extraction of aluminium is cheaper and easier by bauxite not from China clay. In this way, we can say that there are two minerals of aluminium ie, bauxite and China clay but the ore of aluminium is bauxite.

→ Let us consider another example of copper. Copper has various minerals i.e., copper glance (Cu2S), cuprite (Cu2 O), copper pyrites (CuFeS2), malachite (CuCO3 Cu(OH)2) but the ore of copper is copper pyrites (CuFeS2) while others are not. So we can say that, “All the ores are minerals but all the minerals are not ores.”

Types of Ores : Ores can be classified into two main categories. These are :

  • Native ores
  • Combined ores

→ Native Ores : When the elements exist in free or native forms, then they are called native ores. Examples: Ag, Au, Pt etc. When the metals exist in a huge cluster and in pure state then they are called nuggets.

→ Ores in Combined State : In this state, metals react with chlorine, oxygen, sulphur, nitrogen, halogens etc. and form compounds. These compounds are found in earth’s crust. Some examples of various ores of metals in combined state are as follows:

  • Sulphide ores : Here the metals exist in the form of sulphides. Examples: Hg, Pb, Cu, Fe, Zn etc.
  • Oxides ores : Here the metals exist in the form of oxides. Examples : Cu, Al, Zn, Sn, Cr etc.
  • Carbonate ores : Here the metals exist in the form of carbonates. Examples: Ca, Mg, Zn, Cu, Pb, Fe etc.
  • Sulphate ores: Here the metals exist in the form of sulphates. Examples : Ba, Pb, Ca, Mg etc.
  • Halide ores : Here the metals exist in the form of halides. Examples : Na, K, Ag, Ca, Mg, Al etc.
  • Nitrate ores : Here the metals exist in the form of nitrates. Examples : Na, K etc..
    Examples of Ores :

Occurrence of Metals Chemistry Notes

Oxide Ores

  • Cuprite – Cu2O
  • Corrundum – Al2O3
  • Haematite – Fe2O3
  • Bauxite – Al2O3 . 2H2O
  • Pyrolusite – MnO2
  • Cassiterite – SnO2
  • Diaspore – Al2O3 . H2O
  • Magnetite – Fe3O4
  • Zincite – Zno
  • Spinal – MgAl2O4

Sulphide Ores

  • Galena – Pbs
  • Cinnabar – HgS
  • Copper Pyrite – CuFeS2
  • Copper Glance – Cu2S
  • Zinc Blende – Zns
  • Iron Pyrite FeS2
  • Argentite – Ag2S

Carbonate Ores

  • Dolomite – MgCO3 CaCO3
  • Siderite – FeCO3
  • Lime stone СаCO3
  • Calamine – ZnCO3
  • Malachite – CuCO3 . Cu(OH)2
  • Cerrusite – PbCO3
  • Magnesite – MgCO3

Occurrence of Metals Chemistry Notes

Halide Ores

  • Common salt – NaCl
  • Fluorspar – CaF2
  • Horn silver – AgCl
  • Cryolite – AlF3 . 3NaF or Na3AlF6
  • Carnellite – KCl . MgCl2 . 6H2O

Silicate Ores

  • Asbeestos – CaMg3 (SiO3)4
  • Clay – Al2 O3 2SiO2 . 2H2O
  • Spodumene – LiAl(SiO3)2
  • Talc – 3MgO . 4SiO2. 2H2O
  • Potash mica – KH2Al3 (SiO24) 3
  • Beryl – 3BeO . Al2O3 . 6SiO2

Sulphate Ores

  • Epsomite – MgSO4 . 7H2O
  • Gypsum – CaSO4 . 2H2O
  • Barytes – BaSO4
  • Anglesite – PbSO4
  • Selestite – SrSO4

Nitrate Ores

  • Indian nitre – KNO3
  • Chile salt Petre – NaNO3

Table 6.2: Principal ores and minerals of some important metals

Metal Name Composition
Aluminium (Al) Bauxite Al2O3 . 2H2O
Feldspar KAlSi3O8
Cryolite Na3AlF6                   .
Kaolinite [Al2(OH)4Si205]
Corundum Al2O3
Diaspore Al2O3 . H2O
Mica K2O. 3Al2O3 . 6SiO2 2H2O
Iron (Fe) Haematite Fe2O3
Magnetite Fe3O4
Siderite FeCO3
Iron Pyrites (Fool’s gold) FeS2
Limonite Fe2O3 3H2O
Copper (Cu) Copper glance or chalcocite Cu2S
Copper pyrites CuFeS2
Malachite CuCO3 . Cu(OH)2
Cuprite (ruby copper) Cu2O
Azurite 2CuCO3 Cu(OH2)
Zinc (Zn) Zinc blende or sphalerite ZnS
Calamine ZnCO3
Zincite ZnO
Willemite Zn2SiO4
Franklinite ZnO . Fe2O3
Magnesium (Mg) Magnesite MgCO3
Dolomite CaCO3 MgCO3
Epsom salt MgSO4 . 7H2O
Carnallite KCl . MgCl2 . 6H2O
Manganese (Mn) Pyrolusite MnO2
Braunite Mn2O3
Lead (Pb) Galena PbS
Cerrusite PbCO3
Anglesite PbSO4
Calcium (Ca) Limestone or calcite CaCOg
Gypsum CaSO4 . 2H2O
Fluorspar CaF2
Dolomite CaCOg MgCOg
Mercury (Hg) Cinnabar HgS
Silver (Ag) Argentite or silver glance Ag2S
Horn silver AgCl
Sodium (Na) Trona Na2CO3 . 2NaHCO3 . 3H2O
Natron Na2CO3 . H2O
Glauber’s salt Na2SO4 . 10H2O.
Common salt NaCl
Potassium (K) Indian nitre KNO3
Carnallite Sylvine KCl . MgCl2 . 6H2OKCl
Gold (Au) Native metal Au
Titanium (Ti) Rutile TiO2
Ilmenite FeTiO3
Tin (Sn) Cassiterite or Tin stone SnO2
Chromium (Cr) Chromite FeCr2O4

Occurrence of Metals Chemistry Notes

Gangue or Matrix

→ Generally all the ores have some earthly or undesired materials like sand, stone, pebbles etc. in the form of impurities. These impurities are known as gangue or matrix.

Chemistry Notes