Principles and Processes of Isolation of Elements Chemistry Notes
→ All the materials found on the earth crust are made up of different types of elements. Till now about 118 elements are known, out of which nearly 92 occur in nature while the rest are synthetically made in laboratory.
→ A few elements like carbon, sulphur, gold and noble gases occur in free state while others in combined state in the earth crust. Generally metals are highly reactive due to low ionisation enthalpy and high electropositivity. These metals in combined state exist in the form of oxides, carbonates, sulphates, sulphides etc.
→ Most of the elements present in earth have metallic nature. Main source of these elements is earth’s Crust. Among them aluminium (Al) is the most abundant metal (8.3% approx by mass). Iron metal comes after it. Aluminium is the main component of mineral mica. Every substance found on earth is made up of elements.
These elements are divided into three groups:
→ Metals : They are generally solids and are lustrous, malleable, ductile and good conductors of heat and electricity. They have metallic lustre. Out of the known elements, 80% are metal. Examples are Aluminium (AI), Copper (Cu), Iron (Fe), Zinc (Zn), Silver (Ag), Gold (Au), Platinum (Pt) etc.
Table 6.1 : Percentage Quantity of Important Metals
|Calcium (Ca)||j 3.6|
→ Non-Metals : These elements are generally brittle, poor conductors of electricity and non lustrous. Examples are Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N), Halogens (X), Sulphur (S), Phosphorus (P) etc.
→ Metalloids : Those elements which show common characteristics of metals and non-metals are called metalloids. Examples are Boron (B), Silicon (Si), Argenic (As), Antimony (Sb), Tellurium (TI), Bismuth (Bi) etc.
Chapter in Brief :
- Metals exist in combined states are known as minerals.
- The mineral from which the metal can be economically and conveniently extracted is known as ore.
- The process of extracting metals from their ores is called metallurgy.
- The impurities present with ore is known as a gangue or matrix.
- The conversion of huge lamps of ore into powdered form is known as pulverisation
- The process of removal of gangue or matrix from pulverised ore is known as concentration or benefication or ore dressing.
- Hand picking is based on the principle, when ore and gangue particles have different size and colour.
- Gravity separation is based on the principle of difference in densities of ore and gangue particles. It is used for oxide ores.
- Magnetic separation is based on the differences in magnetic properties of the ore components.
- Froth floatation process is based on the principle of difference in the wetting properties of ore and gangue
- particles with water and oil. It is used to concentrate sulphides ores.
- Depressants are used in froth floatation process. They are used to prevent certain types of particles from forming the forth with air bubbles eg., NaCN is used to separate ZnS and PbS.
- Collectors used in froth floatation process are pine oil, eucalyptus oil, fatty acids, xanthates etc.
- Froth stabilizer used in froth floatation process are cresols, aniline etc.
- Leaching is chemical method for concentration. It is used to concentrate those which are soluble in a particular solvent but gangue are not soluble.
- Roasting is a process of heating the concentrated ore strongly in presence of excess of air to convert it into oxide.
- Calcination is a process of heating the concentrated ore either in the absence or limited supply of air to convert it into oxide.
- The process of reducing a metal oxide with coke or some other reducing agent upon heating is known as pyrometallurgy.
- Highly reactive metals are isolated from their ores by electrometallurgy
- The isolation of metal which are presents in soluble complex by the addition of more reactive metal is called hydrometallurgy.
- Pig Iron: The iron obtained from blast furnace has 4% impurities known as pig iron.
- Cast Iron : The iron obtained by pig iron after treatment with scrap of carbon and oxidising it by passing hot air through it. It has 2% impurities.
- Wrought iron or malleable Iron: It is the purest form of iron. It contains carbon and other impurities not more than 0.5%. It is malleable and easily welded.
- Steel: Iron having 0.5% to 1.5% carbon along with small amounts of other elements like Mn, Cr, Ni etc. known as steel.
- The bauxite having oxides of iron as main impurities are known as red bauxite.
- The bauxite having oxides of silicon as main impurities are known as white bauxite.
- Baeyer’s process is used to purify red bauxite.
- Serpeck’s process is used to purify white bauxite.
- The process of extracting a metal by reduction of its oxide with carbon (in from of coke, charcoal as CO) is called smelting
- Iron pyrites (FeS2) is known as fool’s gold.