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.
→ 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 :
- Cuprite – Cu2O
- Corrundum – Al2O3
- Haematite – Fe2O3
- Bauxite – Al2O3 . 2H2O
- Pyrolusite – MnO2
- Cassiterite – SnO2
- Diaspore – Al2O3 . H2O
- Magnetite – Fe3O4
- Zincite – Zno
- Spinal – MgAl2O4
- Galena – Pbs
- Cinnabar – HgS
- Copper Pyrite – CuFeS2
- Copper Glance – Cu2S
- Zinc Blende – Zns
- Iron Pyrite FeS2
- Argentite – Ag2S
- Dolomite – MgCO3 CaCO3
- Siderite – FeCO3
- Lime stone СаCO3
- Calamine – ZnCO3
- Malachite – CuCO3 . Cu(OH)2
- Cerrusite – PbCO3
- Magnesite – MgCO3
- Common salt – NaCl
- Fluorspar – CaF2
- Horn silver – AgCl
- Cryolite – AlF3 . 3NaF or Na3AlF6
- Carnellite – KCl . MgCl2 . 6H2O
- 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
- Epsomite – MgSO4 . 7H2O
- Gypsum – CaSO4 . 2H2O
- Barytes – BaSO4
- Anglesite – PbSO4
- Selestite – SrSO4
- Indian nitre – KNO3
- Chile salt Petre – NaNO3
Table 6.2: Principal ores and minerals of some important metals
|Aluminium (Al)||Bauxite||Al2O3 . 2H2O|
|Diaspore||Al2O3 . H2O|
|Mica||K2O. 3Al2O3 . 6SiO2 2H2O|
|Iron Pyrites (Fool’s gold)||FeS2|
|Copper (Cu)||Copper glance or chalcocite||Cu2S|
|Malachite||CuCO3 . Cu(OH)2|
|Cuprite (ruby copper)||Cu2O|
|Zinc (Zn)||Zinc blende or sphalerite||ZnS|
|Franklinite||ZnO . Fe2O3|
|Epsom salt||MgSO4 . 7H2O|
|Carnallite||KCl . MgCl2 . 6H2O|
|Calcium (Ca)||Limestone or calcite||CaCOg|
|Gypsum||CaSO4 . 2H2O|
|Silver (Ag)||Argentite or silver glance||Ag2S|
|Sodium (Na)||Trona||Na2CO3 . 2NaHCO3 . 3H2O|
|Natron||Na2CO3 . H2O|
|Glauber’s salt||Na2SO4 . 10H2O.|
|Potassium (K)||Indian nitre||KNO3|
|Carnallite Sylvine||KCl . MgCl2 . 6H2OKCl|
|Gold (Au)||Native metal||Au|
|Tin (Sn)||Cassiterite or Tin stone||SnO2|
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.