General Principles & Process of Isolation of Metals – JEE Main Formula Sheet & Class 12 Notes

Ores, Minerals, and Important Ore Examples

Why Ore Identification Is a Direct JEE Main One-Mark Question

A mineral is any naturally occurring substance in the earth's crust that contains a metal. A ore is a mineral from which a metal can be extracted profitably. All ores are minerals but not all minerals are ores. Gangue (or matrix) is the unwanted rocky or earthy material associated with the ore. A flux is a substance added during smelting that reacts with the gangue to form a fusible product called slag, which can be separated from the metal. Acidic gangue requires a basic flux (e.g., limestone CaCO₃) and vice versa.

Important ores tested directly in JEE Main: Aluminium — Bauxite (Al₂O₃·2H₂O, principal ore), Corundum (Al₂O₃), Cryolite (Na₃AlF₆, used as solvent in electrolysis — not the principal ore). Iron — Haematite (Fe₂O₃, most important), Magnetite (Fe₃O₄, magnetic), Limonite (Fe₂O₃·3H₂O), Siderite (FeCO₃), Iron pyrites (FeS₂, fool's gold — not used for iron extraction). Copper — Copper pyrites/Chalcopyrite (CuFeS₂, most important), Malachite (Cu(OH)₂·CuCO₃), Cuprite (Cu₂O), Copper glance (Cu₂S). Zinc — Zinc blende (ZnS, sphalerite), Calamine (ZnCO₃), Zincite (ZnO). Lead — Galena (PbS). Tin — Cassiterite/Tinstone (SnO₂). Silver — argentite/silver glance (Ag₂S), Horn silver (AgCl). Mercury — Cinnabar (HgS). Download the Free PDF for the complete ore-metal identification table.

Concentration of Ores — Physical and Chemical Methods

Why Concentration Methods and Their Principles Are Tested in JEE Main

Concentration (or dressing or beneficiation) removes the gangue to increase the percentage of the metal in the ore. The method used depends on the physical and chemical properties of the ore and the gangue. JEE Main tests both which method is used for which ore and the underlying principle of each method.

Hydraulic washing (gravity separation): Used when the ore particles are denser than gangue. The crushed ore is washed with an upward current of water on a vibrating table — lighter gangue particles are washed away while heavier ore particles settle. Used for tin ore (cassiterite), gold. Magnetic separation: Used when either the ore or gangue is magnetic. A conveyor belt passes the crushed ore over a magnetic roller — magnetic particles are attracted to the roller and fall separately from non-magnetic particles. Used for magnetite (Fe₃O₄, magnetic) to separate from non-magnetic gangue; chromite (FeO·Cr₂O₃) from non-magnetic silica. Froth flotation: Used primarily for sulphide ores. The crushed ore is mixed with water, pine oil (a frothing agent), and collectors (like xanthates or sodium ethyl xanthate). When air is blown through the mixture, sulphide ore particles (which are wetted by pine oil) attach to the froth bubbles and float to the surface while gangue particles (wetted by water) sink. The froth is collected and the ore is recovered. Used for ZnS (zinc blende), Cu₂S, PbS (galena).

Leaching (chemical method): The ore is treated with a suitable chemical reagent that selectively dissolves the metal or its compound. Bayer's process for aluminium: Bauxite is treated with hot concentrated NaOH solution under pressure. Al₂O₃ dissolves as sodium aluminate (NaAlO₂) while impurities (iron oxides, silica already partially dissolved then re-precipitated) are filtered off. The filtrate is diluted and seeded with Al(OH)₃ crystals — aluminium hydroxide precipitates. Heating gives pure Al₂O₃. MacArthur-Forest process for silver and gold: The ore is treated with dilute NaCN solution in the presence of air. Gold dissolves as sodium aurocyanide: 4Au + 8NaCN + 2H₂O + O₂ → 4Na[Au(CN)₂] + 4NaOH. The gold is then recovered by displacing it with zinc: 2Na[Au(CN)₂] + Zn → Na₂[Zn(CN)₄] + 2Au.

Roasting and Calcination — Converting Ores to Oxides

Why the Distinction Between Roasting and Calcination Is a JEE Main Question

Before reduction, most ores are converted to the oxide form because metal oxides are easier to reduce than sulphides or carbonates. Two thermal processes achieve this conversion, and JEE Main frequently tests their distinction.

Calcination is heating the ore strongly in a limited supply of air (or in the absence of air). It is used for carbonate and hydroxide ores. The ore decomposes on heating, releasing CO₂ or H₂O. Examples: ZnCO₃ → ZnO + CO₂; CaCO₃ → CaO + CO₂; Al₂O₃·2H₂O → Al₂O₃ + 2H₂O; Fe₂O₃·3H₂O → Fe₂O₃ + 3H₂O. The product is a porous metal oxide that is easier to reduce.

Roasting is heating the ore strongly in excess of air (with a plentiful oxygen supply). It is used for sulphide ores, which are converted to oxides with the release of SO₂. Examples: 2ZnS + 3O₂ → 2ZnO + 2SO₂; 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂; 4FeS₂ + 11O₂ → 2Fe₂O₃ + 8SO₂; HgS + O₂ → Hg + SO₂ (mercury is directly obtained — its oxide is unstable). Roasting also removes volatile impurities of arsenic and sulphur.

Reduction of Metal Oxides — Methods and Selectivity

Why Reduction Method Selection Is a Reasoning-Based JEE Main Question

After converting the ore to an oxide, the next step is reducing the oxide to the free metal. The choice of reductant depends on the stability of the metal oxide (how strongly the metal holds onto oxygen) and the economics of the process. This is where thermodynamics enters the chapter.

Reduction by carbon (coke): The most widely used method for oxides of moderately active metals — Fe, Zn, Pb, Sn. Coke acts both as fuel and reductant. ZnO + C → Zn + CO; Fe₂O₃ + 3CO → 2Fe + 3CO₂; PbO + C → Pb + CO; SnO₂ + 2C → Sn + 2CO₂. Carbon is cheap and widely available, but it cannot reduce oxides of very reactive metals (Al, Mg, Na) — their oxides are too stable. Reduction by CO (carbon monoxide): In the blast furnace, CO is the primary reducing agent at intermediate temperatures. Fe₂O₃ + 3CO → 2Fe + 3CO₂. CO is generated from coke combustion and the water-gas shift reaction. Reduction by hydrogen: Used when a very pure metal is needed and carbon contamination must be avoided (carbon dissolves in some metals forming carbides). WO₃ + 3H₂ → W + 3H₂O. Also used for reducing CuO to Cu in some processes. Reduction by aluminium (Aluminothermy/Thermite reaction): Aluminium is a more powerful reductant than most metals and can reduce oxides of Cr, Mn, Fe at high temperatures, releasing large amounts of heat. Cr₂O₃ + 2Al → Al₂O₃ + 2Cr + heat; Fe₂O₃ + 2Al → Al₂O₃ + 2Fe + heat (thermite welding of railway tracks). Used when the metal has a very high melting point and would be contaminated by carbon, or when the reaction needs to be self-sustaining.

Self-reduction (auto-reduction): Used for Cu and Pb. When their sulphide ores are partially roasted and the roasted product (oxide) is mixed with the remaining sulphide and heated, the sulphide reduces the oxide: Cu₂S + 2Cu₂O → 6Cu + SO₂; PbS + 2PbO → 3Pb + SO₂. Electrochemical reduction (electrolysis): Used for the most reactive metals — Na, K, Mg, Ca, Al — whose oxides are too stable to be reduced by any chemical reductant economically. Download the Free PDF for a complete reduction method selection table.

Ellingham Diagram — Thermodynamics of Metal Oxide Reduction

Why the Ellingham Diagram Is the Most Conceptual Section in This Chapter for JEE Main

The Ellingham diagram is a plot of ΔG° (standard Gibbs free energy of formation of metal oxides) against temperature for the reaction: (2x/y)M + O₂ → (2/y)MxOy. All curves are written for the same amount of O₂ consumed (one mole of O₂), allowing direct comparison. Since ΔG° = ΔH° – TΔS°, each line has a slope of –ΔS° and an intercept of ΔH° at T = 0.

Key features of the Ellingham diagram: Most metal oxide formation lines have positive slopes (slope = –ΔS° = positive means ΔS° is negative — solid + gas → solid, so entropy decreases). Lines with more negative ΔG° (lower on the diagram) represent more stable oxides. A metal can reduce the oxide of another metal if its oxide line lies below that of the other metal at the temperature of interest — i.e., the reductant has a more negative ΔG° of oxide formation at that temperature.

Carbon lines on the Ellingham diagram: C + O₂ → CO₂ has a nearly horizontal line (slope ≈ 0, because both reactants and products involve one mole of gas — ΔS° ≈ 0). 2C + O₂ → 2CO has a line with a negative slope (ΔG° decreases with increasing T) — this is the unique and critically important feature. As temperature increases, ΔG° for CO formation becomes increasingly negative, meaning CO becomes an increasingly powerful reductant at high temperatures. At temperatures above about 983 K, the CO formation line crosses the CO₂ line, so CO is thermodynamically more stable than CO₂ at high temperatures. This is why blast furnaces operate at very high temperatures — to ensure CO is the dominant and most effective reducing agent.

Why coke reduces iron oxide but not aluminium oxide: On the Ellingham diagram, the line for Al₂O₃ formation lies well below the carbon lines at all practical temperatures — Al₂O₃ has a very large negative ΔG° of formation. The C/CO line can only become more negative than a metal oxide line if the temperature is high enough. For iron oxide, the C/CO line crosses the Fe/Fe₂O₃ line at around 1000 K — carbon can reduce iron oxide above this temperature. For aluminium oxide, the Al/Al₂O₃ line is so far below the carbon lines that no practical temperature allows carbon to reduce it — electrochemical reduction (Hall-Héroult process) is required instead. Download the Free PDF for a simplified Ellingham diagram with key crossing points highlighted.

Blast Furnace — Extraction of Iron

Why Iron Extraction Is a Multi-Step JEE Main Process Question

The blast furnace is a tall cylindrical furnace (approximately 30 m high) used to extract iron from its oxide ores. The charge consists of iron ore (haematite Fe₂O₃ or magnetite Fe₃O₄), coke (carbon fuel and reductant), and limestone (CaCO₃, flux). Hot air blast is blown in from the bottom (tuyeres). The temperature increases from top to bottom: top ≈ 500 K, middle ≈ 900–1300 K, bottom (hearth) ≈ 2100 K.

Reactions in the blast furnace zone by zone: Near the bottom (2100 K): C + O₂ → CO₂ (combustion of coke). CO₂ + C → 2CO (Boudouard reaction — CO is the primary reducing agent at high temperatures). In the middle zone (900–1300 K): Fe₂O₃ + 3CO → 2Fe + 3CO₂ (principal reduction reaction). Flux reaction: CaCO₃ → CaO + CO₂ (calcination of limestone); CaO + SiO₂ → CaSiO₃ (slag formation — calcium silicate is the main slag). Near the top (500 K): 3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂; Fe₃O₄ + CO → 3FeO + CO₂; FeO + CO → Fe + CO₂ (stepwise reduction at lower temperatures using CO). The molten iron (pig iron) sinks to the hearth and is tapped off periodically. The slag floats on top and is also tapped off separately. Pig iron contains about 4% carbon along with other impurities (S, P, Si, Mn) and is further processed to make cast iron, wrought iron, or steel depending on the carbon content required.

Electrochemical Reduction — Hall-Héroult Process for Aluminium

Why Aluminium Extraction by Electrolysis Is a JEE Main Must-Know

Aluminium cannot be extracted by reducing Al₂O₃ with coke (as shown on the Ellingham diagram — Al₂O₃ is too stable). It is extracted by the Hall-Héroult electrolytic process. Pure Al₂O₃ (alumina, obtained from bauxite by Bayer's process) has a very high melting point (2072°C), making direct electrolysis of molten Al₂O₃ impractical. The solution is to dissolve Al₂O₃ in molten cryolite (Na₃AlF₆) with small amounts of fluorspar (CaF₂) added to lower the melting point further. This mixture melts at about 1270 K — much more manageable.

The electrolytic cell uses carbon (graphite) anodes and the steel vessel lined with graphite serves as the cathode. At the cathode: Al³⁺ + 3e⁻ → Al (aluminium is deposited as liquid metal, which sinks to the bottom and is tapped off). At the anode: 2O²⁻ → O₂ + 4e⁻; O₂ + C → CO and CO₂ (the carbon anodes are consumed by oxidation and must be replaced periodically — this is why graphite anodes are used, not permanent metal anodes). The functions of cryolite are to dissolve Al₂O₃, lower the operating temperature, and increase electrical conductivity of the melt. Fluorspar (CaF₂) further lowers the melting point.

Refining of Crude Metals — Methods and Which Metal Uses Which

Why Refining Methods Are the Most-Tested Factual Content in This Chapter

The metal obtained after reduction is crude (impure) and must be refined. The method of refining depends on the nature of the metal and its impurities. JEE Main tests which refining method is used for which metal — this is one of the most direct question types in the chapter.

Distillation: Used for metals with low boiling points that are volatile. The crude metal is heated; it vaporises and is condensed separately from non-volatile impurities. Used for Zinc (b.p. 1180 K) and Mercury (b.p. 630 K). Liquation: Used for metals with low melting points. The crude metal is heated on a sloping hearth; the metal melts and flows away from higher-melting impurities. Used for Tin (Sn), Lead (Pb), Bismuth (Bi). Electrolytic refining: The most widely used method for high-purity metals. The impure metal serves as the anode, pure metal is the cathode, and a solution of the metal salt is the electrolyte. Anode dissolves (anode mud collects precious metal impurities like Ag, Au, Pt), pure metal deposits on cathode. Used for Cu, Ag, Au, Ni, Pb, Al. Anode mud from copper refining often contains precious metals — economically important. Zone refining (fractional crystallisation from melt): Used for ultra-pure semiconductors. A circular heater passes slowly along a rod of the impure metal. Impurities concentrate in the molten zone (since they are more soluble in the melt than in the solid) and move along with the heater to one end, leaving the solidified portion behind in a pure state. Used for Si, Ge, Ga (semiconductor-grade purity). Vapour phase refining: The crude metal is converted to a volatile compound (by reaction with a specific reagent), the volatile compound is purified by fractional distillation, and then decomposed to give pure metal. Two specific processes: Mond process (Nickel): Ni + 4CO → [Ni(CO)₄] (at 330–350 K); [Ni(CO)₄] → Ni + 4CO (at 450–470 K). Tetracarbonylnickel is volatile and easily purified; decomposition gives 99.99% pure nickel. Van Arkel method (Titanium and Zirconium): Ti + 2I₂ → TiI₄ (at ~523 K); TiI₄ → Ti + 2I₂ (on a hot tungsten filament at ~1700 K). Also used for Zr. Chromatographic separation: Used when different components of a mixture have different adsorption affinities for a stationary phase. Column chromatography can be used for rare earth elements. Download the Free PDF for the complete refining method table with metal examples.