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.

→ 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 :

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

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

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