ChemistryCBSE Class 12

General Principles and Processes of Isolation of Elements Class 12 (School-Assessed)

Updated 14 October 2026 · Fact-checked

Assessed in school only, not in the board exam. Assessed only formatively in school, not in the board exam; taught from the CBSE reading material.

General Principles and Processes of Isolation of Elements is taught in CBSE Class 12 Chemistry for 2026-27 from the CBSE reading material and assessed in school only, not in the board exam. It explains how metals are obtained from ores: concentration, conversion to oxide, reduction, electrolysis and refining, with India's metallurgical history.

What General Principles and Processes of Isolation of Elements is about

Metals are rarely found free in nature. Most occur as compounds in minerals, and the few minerals from which a metal can be extracted profitably are called ores. The whole process of getting a pure metal from its ore is metallurgy.

For 2026-27 this topic is in the CBSE Class 12 syllabus for formative (school) assessment only, taught from the CBSE reading material adapted from the older NCERT book. It is not in the board exam, but it connects with Electrochemistry (electrolytic refining), the d-block chapter (transition metals) and Coordination Compounds (cyanide and carbonyl complexes).

The reading material begins with India's long metallurgical tradition: copper from the Khetri mines, the deep ancient gold mines of Maski, iron smelting in the Ganga plains from about 1800 BCE, wootz steel, the rust-free Iron Pillar of Delhi and the 'downward' distillation of zinc at Zawar.

The chemistry follows three steps:
1. Concentration of the ore (removing gangue): hydraulic washing, magnetic separation, froth floatation and leaching.
2. Isolation of the crude metal: converting the ore to an oxide by calcination or roasting, then reducing the oxide (or using electrolysis).
3. Refining the crude metal: distillation, liquation, electrolytic refining, zone refining, vapour phase refining (Mond and van Arkel methods) and chromatography.

It ends with uses of aluminium, copper, zinc and iron.

In real board papers: not asked in any of the 8 board papers we hold (2023 to 2026). See the questions

Key concepts

Occurrence of metals, minerals and ores

NCERT section CBSE reading material: General Principles and Processes of Isolation of Elements (introduction); 6.1 Occurrence of Metals

A few elements such as carbon, sulphur, gold and the noble gases occur free; the rest occur combined in the earth's crust. Aluminium is the most abundant metal (about 8.3% by weight, the third most abundant element); iron is the second most abundant metal. Gems such as ruby and sapphire are impure Al₂O₃ (with Cr and Co respectively).

Minerals: naturally occurring chemical substances obtained by mining.
Ores: minerals from which a metal can be extracted profitably.
Gangue: earthy or unwanted material mixed with the ore.
Metallurgy: the whole scientific and technological process of isolating a metal from its ore.

The ore chosen must make extraction chemically feasible and commercially viable: bauxite for aluminium; for iron, oxide ores (abundant and not producing polluting SO₂, as iron pyrites would).

India's metallurgy (reading material): native copper bead from Mehrgarh (about 6000 BCE); copper from chalcopyrite of the Aravalli hills used by Chalcolithic cultures; deepest ancient gold mines at Maski, Karnataka; iron smelting in the Vindhyas and Ganga plains from around 1800 BCE; wootz steel (1.0–1.9% carbon) exported widely; the Delhi Iron Pillar of wrought iron, uncorroded for about 1,600 years; and zinc distillation at Zawar, Rajasthan, where India was the first to master zinc distillation.

Concentration of ores

NCERT section CBSE reading material: 6.2 Concentration of Ores (6.2.1 Hydraulic Washing; 6.2.2 Magnetic Separation; 6.2.3 Froth Floatation; 6.2.4 Leaching)

Removing gangue is called concentration, dressing or benefaction. The method depends on differences in physical properties between the ore and the gangue.

Hydraulic washing (gravity separation): an upward stream of water washes away the lighter gangue and leaves the heavier ore particles.
Magnetic separation: used when either the ore or the gangue is magnetic (iron ores). The powdered ore falls on a belt over a magnetic roller; the magnetic part stays close to the belt.
Froth floatation: used for sulphide ores. The powdered ore is suspended in water with collectors (pine oil, fatty acids, xanthates), which make the mineral particles non-wettable by water, and froth stabilisers (cresols, aniline). The mineral particles are wetted by oil and the gangue by water. A rotating paddle draws in air; the froth carries the mineral particles to the top, where it is skimmed off. Depressants separate two sulphides: NaCN keeps ZnS out of the froth while PbS rises with it. (The reading material tells how a washerwoman's observation of copper compounds caught in soapsuds led to this method.)
Leaching: dissolving the ore in a suitable solvent.
Bauxite: heated with concentrated NaOH at 473–523 K and 35–36 bar (digestion); Al₂O₃ dissolves as sodium aluminate (SiO₂ dissolves as silicate). CO₂ is passed in, and adding a little fresh hydrated alumina (seeding) precipitates hydrated Al₂O₃, which is heated to give pure Al₂O₃.
Silver and gold: leached with dilute NaCN or KCN in the presence of air (oxygen) to form soluble cyanide complexes; the metal is then displaced by zinc.

Extraction of crude metal: calcination, roasting and reduction

NCERT section CBSE reading material: 6.3 Extraction of Crude Metal from Concentrated Ore

Before reduction, the concentrated ore is usually converted to an oxide, because oxides are easier to reduce.

Calcination: heating to remove volatile matter, leaving the oxide. For example, a carbonate loses CO₂: $Z n C O_{3} \to Z n O + C O_{2}$ ; hydrated oxides lose water.
Roasting: heating the ore in a regular supply of air at a temperature below the melting point of the metal. It is used for sulphide ores:

$2 Z n S + 3 O_{2} \to 2 Z n O + 2 S O_{2}$
$2 P b S + 3 O_{2} \to 2 P b O + 2 S O_{2}$
$2 C u_{2} S + 3 O_{2} \to 2 C u_{2} O + 2 S O_{2}$

Reduction then converts the oxide to the metal, using a reducing agent such as carbon (coke) or carbon monoxide, or a more reactive metal: $Z n O + C \to Z n + C O$ . For very reactive metals such as aluminium, reduction by chemicals is not practical, and electrolysis of the molten compound is used instead (an electrolytic method). The choice of method rests on thermodynamic and electrochemical principles: the reduction must have a negative Gibbs energy change under the conditions used.

Refining: distillation, liquation and electrolytic refining

NCERT section CBSE reading material: 6.4 Refining (a) Distillation (b) Liquation (c) Electrolytic refining

Crude metal contains impurities, so it is refined by a method that suits the properties of the metal and the impurity.

Distillation: for low-boiling metals such as zinc and mercury; the metal is evaporated and collected as a pure distillate.
Liquation: a low-melting metal such as tin is made to flow down a sloping surface, leaving higher-melting impurities behind.
Electrolytic refining: the impure metal is the anode, a strip of pure metal is the cathode, and the electrolyte is a soluble salt of the same metal. The more basic metals stay in solution and the less basic ones collect below the anode as anode mud.

For copper: anodes of impure (blister) copper, cathodes of pure copper, electrolyte of acidified copper sulphate. Copper dissolves at the anode ( $C u \to C u^{2 +} + 2 e^{-}$ ) and is deposited at the cathode ( $C u^{2 +} + 2 e^{-} \to C u$ ). The anode mud contains antimony, selenium, tellurium, silver, gold and platinum, whose recovery can pay for the refining. Zinc can be refined in the same way.

Refining: zone refining, vapour phase refining and chromatography

NCERT section CBSE reading material: 6.4 Refining (d) Zone refining (e) Vapour phase refining (f) Chromatographic methods

Zone refining: based on the fact that impurities are more soluble in the melt than in the solid metal. A heater moves slowly along a rod of impure metal, creating a molten zone. As the heater moves on, pure metal crystallises behind it and the impurities move into the new molten zone. Repeating this many times in the same direction drives the impurities to one end, which is cut off. It gives very high purity metals, especially semiconductors: germanium, silicon, boron, gallium and indium.
Vapour phase refining: the metal is converted to a volatile compound, which is collected and decomposed to give the pure metal. Two conditions: the metal must form a volatile compound with an available reagent, and that compound must decompose easily.
Mond process for nickel: nickel heated in a stream of CO forms volatile nickel tetracarbonyl, which decomposes at a higher temperature to give pure nickel: $N i + 4 C O \to N i (C O)_{4}$ ; $N i (C O)_{4} \to N i + 4 C O$ .
van Arkel method for zirconium or titanium: removes oxygen and nitrogen impurities. The crude metal is heated with iodine in an evacuated vessel; the more covalent metal iodide volatilises and is decomposed on a tungsten filament heated electrically to about 1800 K, where pure metal deposits: $Z r + 2 I_{2} \to Z r I_{4}$ ; $Z r I_{4} \to Z r + 2 I_{2}$ .
Chromatographic methods: column chromatography purifies elements available in tiny amounts when impurities are chemically very similar to the element.

Uses of aluminium, copper, zinc and iron

NCERT section CBSE reading material: 6.5 Uses of Aluminium, Copper, Zinc and Iron

Aluminium: foil for wrapping food; fine dust in paints and lacquers; reducing agent for extracting chromium and manganese from their oxides; electrical wires; light alloys.
Copper: electrical wires, water and steam pipes; alloys tougher than the metal: brass (with zinc), bronze (with tin), coinage alloy (with nickel).
Zinc: galvanising iron; batteries; alloys such as brass (60% copper, 40% zinc) and german silver (nickel 40–50%, with roughly equal shares of copper and zinc making up the rest); and, as zinc dust, a reducing agent for making dyes and paints.
Iron: cast iron for stoves, railway sleepers, gutter pipes and toys, and for making wrought iron and steel; wrought iron for anchors, wires, bolts, chains and farm tools; steel and alloy steels: nickel steel (cables, automobile and aeroplane parts, pendulums, measuring tapes), chrome steel (cutting tools, crushing machines) and stainless steel (cycles, automobiles, utensils, pens).

Chemistry in real life: General Principles and Processes of Isolation of Elements

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Concentration of ores

Suppose a mining company has a low-grade copper sulphide ore mixed with lots of sand and rock.

Which concentration method suits this ore, and how does it work?

Try it first, then show the solutionSolution

Sulphide ores are concentrated by froth floatation.
The powdered ore is mixed with water, a collector such as pine oil and a froth stabiliser; the sulphide particles are wetted by oil and the gangue by water.
Air blown in by a rotating paddle forms froth that carries the sulphide particles to the top, where it is skimmed off; the sand sinks.

Answer: Froth floatation: oil-wetted sulphide particles rise with the froth and are skimmed off, while water-wetted gangue sinks.

Memory hook: Sulphides float, sand sinks.

Refining: distillation, liquation and electrolytic refining

Imagine a copper refinery where the sludge collecting under the anodes is sold at a profit.

Explain how copper is refined electrolytically and why the sludge is valuable.

Try it first, then show the solutionSolution

Impure copper is the anode, pure copper strips are the cathode, and the electrolyte is acidified copper sulphate.
Copper dissolves at the anode and deposits as pure copper on the cathode.
Less reactive impurities such as silver, gold and platinum fall as anode mud; recovering them can pay for the refining.

Answer: Copper moves from the impure anode to the pure cathode; precious metals in the anode mud are recovered.

Memory hook: Copper crosses over; the treasure falls below.

Refining: zone refining, vapour phase refining and chromatography

Suppose an electronics company needs silicon so pure that only a few impurity atoms in a billion are allowed.

Which refining method is used and on what principle?

Try it first, then show the solutionSolution

Zone refining is used for semiconductors such as silicon and germanium.
Impurities are more soluble in the molten metal than in the solid.
A moving heater sweeps the molten zone, and the impurities, along the rod to one end, which is cut off; repeating gives very high purity.

Answer: Zone refining, because impurities prefer the melt and are swept to one end of the rod.

Memory hook: Impurities follow the heat.

Occurrence of metals, minerals and ores

Imagine you visit the Iron Pillar in Delhi and wonder how it has stood for about 1,600 years without rusting.

What does the reading material say about the pillar's material and what it shows about ancient Indian metallurgy?

Try it first, then show the solutionSolution

The pillar is made of wrought iron, obtained by hot forging porous 'sponge iron' made by reducing iron ore with charcoal.
It contains small amounts of C, Si, Mn, P, Ni, Cu and N besides iron.
Its resistance to corrosion over about 1,600 years shows the advanced skill of ancient Indian iron workers.

Answer: It is wrought iron of a special composition; its lack of corrosion shows the high skill of ancient Indian metallurgy.

Memory hook: Delhi's pillar: wrought iron that never rusted.

Topics in this chapter

General Principles and Processes of Isolation of Elements formula sheet

Leaching of bauxite: $A l_{2} O_{3} + 2 N a O H + 3 H_{2} O \to 2 N a [A l (O H)_{4}]$; Digestion at 473–523 K and 35–36 bar.
Precipitation of alumina: $2 N a [A l (O H)_{4}] + 2 C O_{2} \to A l_{2} O_{3} \cdot 3 H_{2} O + 2 N a H C O_{3}$; The reading material writes the hydrated alumina as Al₂O₃·xH₂O; it is shown here with x = 3 so the equation balances. Seeding with fresh hydrated alumina helps precipitation.
Cyanide leaching of silver or gold: $4 M + 8 C N^{-} + 2 H_{2} O + O_{2} \to 4 [M (C N)_{2}]^{-} + 4 O H^{-}$; M = Ag or Au; then $2 [M (C N)_{2}]^{-} + Z n \to [Z n (C N)_{4}]^{2 -} + 2 M$ .
Calcination: $Z n C O_{3} \to Z n O + C O_{2}$; Heating to remove volatile matter.
Roasting of sulphide ores: $2 Z n S + 3 O_{2} \to 2 Z n O + 2 S O_{2}$; Also $2 P b S + 3 O_{2} \to 2 P b O + 2 S O_{2}$ and $2 C u_{2} S + 3 O_{2} \to 2 C u_{2} O + 2 S O_{2}$ .
Reduction with carbon: $Z n O + C \to Z n + C O$; Coke as reducing agent.
Mond process: $N i + 4 C O \to N i (C O)_{4}$; The volatile carbonyl decomposes at a higher temperature: $N i (C O)_{4} \to N i + 4 C O$ .
van Arkel method: $Z r + 2 I_{2} \to Z r I_{4}$; Decomposed on a tungsten filament at about 1800 K: $Z r I_{4} \to Z r + 2 I_{2}$ .

Tricks to remember General Principles and Processes of Isolation of Elements

Short memory aids. Say each one aloud once, then use it on a question the same day.

C-I-R: Concentrate, Isolate, Refine
Every extraction follows C-I-R: concentrate the ore, isolate the crude metal, refine it.
Use it when: Outlining any metallurgy answer.
Calcination without air, Roasting with air
Calcination just heats off volatiles (carbonates, hydrates); Roasting needs a Regular supply of air (sulphides).
Use it when: Telling the two processes apart.
Mond = Monoxide; van Arkel = iodine
Mond uses carbon monoxide for nickel; van Arkel uses iodine for zirconium and titanium.
Use it when: Vapour phase refining.
Zone refining for semiconductors
Ge, Si, B, Ga, In: 'Great Silicon Brings Gadgets In'.
Use it when: Listing metals refined by zone refining.

General Principles and Processes of Isolation of Elements: previous year questions

Not asked in any of the 8 board papers we hold (2023 to 2026).

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is the difference between a mineral and an ore?Show answer
A mineral is any naturally occurring substance mined from the earth; an ore is a mineral from which a metal can be extracted profitably.
2.What is gangue?Show answer
Earthy or unwanted material mixed with the ore.
3.Which concentration method is used for sulphide ores?Show answer
Froth floatation.
4.What does NaCN do in froth floatation of a ZnS–PbS ore?Show answer
It acts as a depressant, keeping ZnS out of the froth while PbS rises with it.
5.What is digestion in the leaching of bauxite?Show answer
Heating powdered bauxite with concentrated NaOH at 473–523 K and 35–36 bar to dissolve Al₂O₃ as sodium aluminate.
6.What is roasting?Show answer
Heating an ore in a regular supply of air below the melting point of the metal, usually to convert sulphides to oxides.
7.What collects in the anode mud during copper refining?Show answer
Antimony, selenium, tellurium, silver, gold and platinum.
8.On what principle is zone refining based?Show answer
Impurities are more soluble in the melt than in the solid metal.
9.Which method refines zirconium and titanium?Show answer
The van Arkel method (iodide formation and decomposition on a hot tungsten filament).

Best order to study it

Read the introduction on Indian metallurgy and learn the terms mineral, ore, gangue and metallurgy.
Learn the four concentration methods, with froth floatation and bauxite leaching in detail.
Learn calcination, roasting and reduction with their equations.
Learn the refining methods: distillation, liquation, electrolytic, zone, vapour phase (Mond, van Arkel) and chromatography.
Finish with the uses of aluminium, copper, zinc and iron.

Quick revision checklist

The night before the exam: can you do each of these without looking?

Can you name the three main steps of metallurgy?
Can you describe froth floatation, naming a collector, a froth stabiliser and a depressant?
Can you write the equations for leaching of bauxite and of silver or gold?
Can you distinguish calcination and roasting with one equation each?
Can you describe electrolytic refining of copper with electrode reactions?
Can you explain zone refining and name two metals refined by it?
Can you write the Mond and van Arkel equations?
Can you give two uses each of Al, Cu, Zn and Fe?

General Principles and Processes of Isolation of Elements: frequently asked questions

Is Isolation of Elements in the CBSE Class 12 board exam for 2026-27?

No. The 2026-27 syllabus lists General Principles and Processes of Isolation of Elements as a topic assessed only formatively in school. It is taught from the CBSE reading material and may appear in school tests or projects, but not in the board paper.

Why are sulphide ores roasted before reduction?

Oxides are easier to reduce than sulphides, so the sulphide is heated in air to convert it to the oxide, which is then reduced to the metal.

What is the difference between Mond process and van Arkel method?

Both are vapour phase refining methods. The Mond process refines nickel through volatile Ni(CO)₄ formed with carbon monoxide. The van Arkel method refines zirconium or titanium through volatile iodides, which are decomposed on a hot tungsten filament.

Why is cyanide used in the extraction of gold and silver?

In the presence of air, dilute NaCN or KCN dissolves gold and silver as soluble cyanide complexes, separating them from the rock. Zinc then displaces the metal from the complex.

Based on: CBSE Chemistry (043) syllabus 2026-27; CBSE Chemistry reading material, Class XII (2026-27)