Unit 7

Inorganic Chemistry

Class 12 Chemistry

Studies of Heavy Metals

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NEB/CDC syllabus scope: Unit 7 is a 15-teaching-hour inorganic chemistry unit covering copper, zinc, mercury, iron and silver. The required study includes specified occurrence and extraction methods, selected chemical properties and uses, blue vitriol, red and black oxides of copper, white vitriol, calomel, corrosive sublimate, manufacture of steel by Basic Oxygen and Open Hearth methods, corrosion of iron and its prevention, cyanide extraction of silver, silver chloride and silver nitrate.

1. Introduction

Heavy metals in this chapter The term “heavy metal” is used here in the traditional school-textbook sense for relatively dense metallic elements studied through their ores, extraction, properties, compounds and practical uses. The NEB chapter specifically focuses on Cu, Zn, Hg, Fe and Ag.

Metal	Important ore in this chapter	Main extraction process studied	Important compound/topic
Copper (Cu)	Copper pyrite, CuFeS₂	Concentration → roasting/smelting → conversion	Blue vitriol, CuSO₄·5H₂O; Cu₂O; CuO
Zinc (Zn)	Zinc blende, ZnS	Roasting to ZnO → reduction → condensation	White vitriol, ZnSO₄·7H₂O
Mercury (Hg)	Cinnabar, HgS	Roasting and condensation of Hg vapour	Calomel, Hg₂Cl₂; corrosive sublimate, HgCl₂
Iron (Fe)	Haematite, Fe₂O₃	Blast furnace reduction	Steel manufacture; corrosion
Silver (Ag)	Argentite, Ag₂S	Cyanide leaching and displacement	AgCl and AgNO₃

Diagram 1: Chapter map of Cu, Zn, Hg, Fe and Ag

2. Copper (Cu)

Atomic symbol: CuImportant oxidation states: +1, +2

2.1 Occurrence

Copper occurs both in the native state and in combined form. The ore specifically required in this syllabus is copper pyrite or chalcopyrite, CuFeS₂.

Ore / mineral	Formula	Comment
Copper pyrite / chalcopyrite	CuFeS₂	Main extraction ore studied in this chapter
Cuprite	Cu₂O	Oxide mineral
Malachite	CuCO₃·Cu(OH)₂	Basic copper carbonate mineral

2.2 Extraction of Copper from Copper Pyrite

The essential stages are concentration, roasting/smelting, removal of iron impurity as slag, conversion of copper sulphide to blister copper, and purification where required.

Diagram 2: Simplified extraction flow sheet for copper pyrite

Step 1: Concentration

Because copper pyrite is a sulphide ore, it is commonly concentrated by froth flotation, which separates sulphide particles from much of the gangue.

Step 2: Roasting and Formation of Matte

Partial oxidation converts iron sulphide more readily to oxide while much copper remains as copper(I) sulphide.

2CuFeS₂ + O₂ → Cu₂S + 2FeS + SO₂ 2FeS + 3O₂ → 2FeO + 2SO₂

Step 3: Removal of Iron as Slag

Silica acts as an acidic flux and combines with FeO:

FeO + SiO₂ → FeSiO₃

The molten iron silicate forms a separate slag layer.

Step 4: Conversion to Copper

Part of the copper(I) sulphide is oxidized to copper(I) oxide:

2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂

Then self-reduction occurs:

2Cu₂O + Cu₂S → 6Cu + SO₂

Why “blister copper”? Escaping sulphur dioxide produces a blistered surface on the crude copper. Further refining may be used when high-purity copper is required, especially for electrical applications.

2.3 Chemical Properties of Copper

With Air / Oxygen

2Cu + O₂ → 2CuO

Copper(II) oxide, CuO, is black. In moist air containing CO₂, a green basic copper carbonate patina may develop slowly.

2Cu + O₂ + CO₂ + H₂O → CuCO₃·Cu(OH)₂

With Acids

Copper lies below hydrogen in the activity series and does not liberate H₂ from ordinary dilute non-oxidizing acids. It reacts with oxidizing acids.

Cu + 2H₂SO₄(conc.) → CuSO₄ + SO₂ + 2H₂O 3Cu + 8HNO₃(dil.) → 3Cu(NO₃)₂ + 2NO + 4H₂O Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O

With Aqueous Ammonia

A small amount of ammonia can precipitate pale-blue copper(II) hydroxide from a Cu²⁺ solution, while excess ammonia produces the characteristic deep-blue ammine complex.

Cu²⁺ + 2NH₃ + 2H₂O → Cu(OH)₂↓ + 2NH₄⁺ Cu²⁺ + 4NH₃ ⇌ [Cu(NH₃)₄]²⁺

With Metal Ions

Copper can reduce ions of less reactive metals such as Ag⁺:

Cu + 2Ag⁺ → Cu²⁺ + 2Ag

Exam Important The “aqueous ammonia” test is frequently asked. Remember the sequence: light-blue Cu(OH)₂ precipitate first, then deep-blue ammine complex in excess NH₃.

2.4 Uses of Copper

Electrical wiring, motors and generators because of high electrical conductivity.
Heat exchangers and cookware because of good thermal conductivity.
Alloys such as brass and bronze.
Plumbing and architectural applications.

2.5 Blue Vitriol — CuSO₄·5H₂O

Blue vitriol Blue vitriol is hydrated copper(II) sulphate, CuSO₄·5H₂O, which forms characteristic blue crystals.

Preparation

Copper(II) oxide or copper(II) carbonate can be treated with dilute sulphuric acid, followed by concentration and crystallization.

CuO + H₂SO₄ → CuSO₄ + H₂O CuSO₄ + 5H₂O → CuSO₄·5H₂O

Properties

Blue crystalline solid, soluble in water.
On strong heating it loses water of crystallization and forms nearly white anhydrous CuSO₄.

CuSO₄·5H₂O → CuSO₄ + 5H₂O

With sodium hydroxide:

CuSO₄ + 2NaOH → Cu(OH)₂↓ + Na₂SO₄

Diagram 3: Hydrated and anhydrous copper(II) sulphate

Uses

Laboratory reagent and source of Cu²⁺ ions.
Used in some fungicidal formulations such as Bordeaux mixture.
Anhydrous CuSO₄ can be used as a qualitative test for water because it becomes blue on hydration.
Used in electroplating/electrorefining electrolytes.

2.6 Red and Black Oxides of Copper

Compound	Formula	Colour	Uses
Copper(I) oxide / red oxide	Cu₂O	Red	Pigments, antifouling coatings and semiconductor applications
Copper(II) oxide / black oxide	CuO	Black	Pigments, ceramics, catalyst/oxidation applications and preparation of copper salts

3. Zinc (Zn)

Atomic symbol: ZnCommon oxidation state: +2

3.1 Occurrence

The principal ore specified by the syllabus is zinc blende or sphalerite, ZnS. Other zinc minerals include calamine/smithsonite (ZnCO₃) and zincite (ZnO).

3.2 Extraction of Zinc from Zinc Blende

Diagram 4: Extraction of zinc from zinc blende

Roasting

2ZnS + 3O₂ → 2ZnO + 2SO₂

Reduction

ZnO + C → Zn + CO

Carbon monoxide can also act as a reducing agent under suitable furnace conditions:

ZnO + CO → Zn + CO₂

Important process point At the high reduction temperature, zinc is produced as vapour. It must be cooled and condensed to collect the metal.

3.3 Properties of Zinc

With Air

2Zn + O₂ → 2ZnO

ZnO is yellow when hot and becomes white on cooling.

With Acids

Zn + 2HCl → ZnCl₂ + H₂↑ Zn + H₂SO₄(dil.) → ZnSO₄ + H₂↑

With Alkali

Zinc is amphoteric and dissolves in strong alkali, forming a zincate complex and hydrogen.

Zn + 2NaOH + 2H₂O → Na₂[Zn(OH)₄] + H₂↑

Displacement Reaction

Zn + CuSO₄ → ZnSO₄ + Cu

3.4 Uses of Zinc

Galvanizing iron and steel to reduce corrosion.
Manufacture of brass and other alloys.
Dry cells and batteries.
Die-casting and protective metal coatings.

3.5 White Vitriol — ZnSO₄·7H₂O

White vitriol White vitriol is hydrated zinc sulphate, ZnSO₄·7H₂O.

Preparation

Zn + H₂SO₄(dil.) → ZnSO₄ + H₂↑

Concentration and crystallization of the solution give hydrated zinc sulphate crystals.

ZnSO₄ + 7H₂O → ZnSO₄·7H₂O

Properties

Colourless crystalline solid and soluble in water.
Loses water of crystallization on heating.
Gives a white Zn(OH)₂ precipitate with NaOH; the precipitate dissolves in excess NaOH because Zn(OH)₂ is amphoteric.

ZnSO₄ + 2NaOH → Zn(OH)₂↓ + Na₂SO₄ Zn(OH)₂ + 2OH⁻ → [Zn(OH)₄]²⁻

Uses

Laboratory source of Zn²⁺.
Electrolytes and electroplating-related applications.
Used in textile, chemical and zinc-compound manufacture.
Used as a micronutrient source in controlled agricultural formulations.

Diagram 5: Zinc shows amphoteric behaviour

4. Mercury (Hg)

Atomic symbol: HgLiquid metal at room temperature

4.1 Occurrence

The principal ore required by the syllabus is cinnabar, HgS.

4.2 Extraction of Mercury from Cinnabar

Concentrated cinnabar is roasted in air. Mercury is released as vapour and then condensed.

HgS + O₂ → Hg + SO₂

The process can also be represented through temporary oxide formation:

2HgS + 3O₂ → 2HgO + 2SO₂ 2HgO → 2Hg + O₂

Diagram 6: Simplified extraction of mercury from cinnabar

4.3 Properties of Mercury

Silvery, dense liquid metal at ordinary room temperature.
Forms alloys called amalgams with many metals.
Does not readily react with dilute HCl or dilute H₂SO₄.
Reacts with oxidizing acids such as nitric acid.
Combines with sulphur to form mercury sulphide.

Hg + S → HgS

Safety / Remember Mercury and many mercury compounds are toxic. Their historical laboratory or medical uses should not be interpreted as instructions for personal handling or treatment. Modern handling requires appropriate safety controls.

4.4 Calomel — Hg₂Cl₂

Calomel Calomel is mercury(I) chloride, Hg₂Cl₂, a sparingly soluble white solid.

Preparation

One simple preparation is the combination of corrosive sublimate with metallic mercury:

HgCl₂ + Hg → Hg₂Cl₂

Important Property

With ammonia, calomel becomes dark because metallic mercury is produced along with an amidochloride product:

Hg₂Cl₂ + 2NH₃ → Hg + HgNH₂Cl + NH₄Cl

Uses

Used in the calomel reference electrode in electrochemistry.
Historically used in medicine, but such uses are obsolete or restricted because of mercury toxicity.

Diagram 7: Practical application of calomel in a reference electrode

4.5 Corrosive Sublimate — HgCl₂

Corrosive sublimate Corrosive sublimate is mercury(II) chloride, HgCl₂, a highly toxic mercury compound.

Preparation

Hg + Cl₂ → HgCl₂

Properties

White crystalline compound.
More soluble than calomel.
Highly poisonous and corrosive; it must not be handled casually.
Can be reduced stepwise to Hg₂Cl₂ and then to Hg in classical qualitative chemistry reactions.

Uses

Historically used as a disinfectant/preservative; such uses are now strongly limited because of toxicity.
Used as a chemical reagent and in specialized industrial chemistry under controlled conditions.

Feature	Calomel	Corrosive sublimate
Formula	Hg₂Cl₂	HgCl₂
Mercury oxidation state	+1 average per Hg atom	+2
Solubility	Sparingly soluble	More soluble
Important use	Reference electrode	Chemical reagent; historical disinfectant use
Safety	Both require careful handling because mercury compounds are toxic.

5. Iron (Fe)

Atomic symbol: FeCommon oxidation states: +2, +3

5.1 Occurrence

Iron occurs widely in combined form. Important ores include haematite (Fe₂O₃), magnetite (Fe₃O₄), siderite (FeCO₃) and iron pyrites (FeS₂). The blast-furnace extraction is commonly explained using haematite.

5.2 Extraction of Iron in the Blast Furnace

The blast furnace is charged with iron ore, coke and limestone. Hot air is blown near the bottom. Carbon monoxide formed in the furnace acts as the principal reducing gas for iron oxides.

Diagram 8: Simplified blast furnace

Formation of Carbon Monoxide

C + O₂ → CO₂ CO₂ + C → 2CO

Reduction of Iron Oxide

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Function of Limestone

CaCO₃ → CaO + CO₂

Calcium oxide acts as a basic flux and removes silica:

CaO + SiO₂ → CaSiO₃

Molten calcium silicate forms slag and floats above the denser molten iron.

Exam Important In a blast-furnace answer, identify the roles clearly: coke = fuel/reducing-gas source; limestone = flux; CO = reducing agent; CaSiO₃ = slag.

5.3 Properties of Iron

Iron is a strong, magnetic metal that readily forms Fe²⁺ and Fe³⁺ compounds.

With Oxygen

3Fe + 2O₂ → Fe₃O₄

With Dilute Acids

Fe + 2HCl → FeCl₂ + H₂↑

With Steam

3Fe + 4H₂O(g) → Fe₃O₄ + 4H₂

With Chlorine

2Fe + 3Cl₂ → 2FeCl₃

5.4 Uses of Iron

Construction, machinery, vehicles, tools and infrastructure.
Primary raw material for steel production.
Magnetic and engineering applications.
Cast iron and alloy steels for specialized mechanical properties.

5.5 Manufacture of Steel

A. Basic Oxygen Method (Basic Oxygen Furnace / BOF)

Molten iron is charged with scrap and basic flux. High-purity oxygen is blown rapidly into the molten metal. Carbon and other impurities are oxidized, while lime helps transfer acidic oxides such as SiO₂ and P₂O₅ into the slag.

C + O₂ → CO₂ Si + O₂ → SiO₂ 2Mn + O₂ → 2MnO 4P + 5O₂ → 2P₂O₅ CaO + SiO₂ → CaSiO₃ 3CaO + P₂O₅ → Ca₃(PO₄)₂

Diagram 9: Basic Oxygen Method

B. Open Hearth Process

In the open hearth process, pig iron and scrap are heated in a broad regenerative furnace. Oxidizing conditions reduce carbon and other impurities, and slag-forming materials remove unwanted oxides. The process is much slower than the Basic Oxygen Method and is now historically important rather than dominant in modern steelmaking.

Feature	Basic Oxygen Method	Open Hearth Process
Oxidizing agent	High-purity oxygen blown into melt	Oxidizing furnace atmosphere / ore additions
Speed	Fast	Slow
Heat source	Oxidation reactions contribute strongly	Regenerative furnace heating
Modern status	Widely important	Largely historical / obsolete industrially

5.6 Corrosion of Iron and Its Prevention

Rusting Rusting is the electrochemical corrosion of iron in the presence of moisture and oxygen, producing hydrated iron(III) oxide, commonly represented approximately as Fe₂O₃·xH₂O.

Electrochemical Steps

At an anodic region:

Fe → Fe²⁺ + 2e⁻

At a cathodic region in aerated neutral water:

O₂ + 2H₂O + 4e⁻ → 4OH⁻

Then:

Fe²⁺ + 2OH⁻ → Fe(OH)₂

Further oxidation produces Fe(III) hydroxide/oxyhydroxide species that ultimately form hydrated rust.

Diagram 10: Electrochemical mechanism of rusting

Prevention of Corrosion

Method	Principle	Example
Painting / polymer coating	Blocks water and oxygen	Bridges, machinery
Oiling / greasing	Forms temporary barrier	Tools and moving parts
Galvanizing	Zinc coating protects and can act sacrificially	Roofing sheets, pipes
Electroplating	Protective metal coating	Cr/Ni-coated steel
Alloying	Produces more corrosion-resistant material	Stainless steel containing Cr
Cathodic protection	Iron is forced to act as cathode	Pipelines, tanks, ship structures

6. Silver (Ag)

Atomic symbol: AgCommon oxidation state: +1

6.1 Occurrence

Silver can occur native and in ores. The syllabus specifically asks for extraction by the cyanide process, commonly described using argentite, Ag₂S.

6.2 Extraction of Silver by Cyanide Process

Finely powdered silver ore is treated with dilute cyanide solution in the presence of air/oxygen. Silver forms a soluble dicyanoargentate(I) complex. Zinc then displaces metallic silver from the solution.

Leaching

Ag₂S + 4NaCN ⇌ 2Na[Ag(CN)₂] + Na₂S

Precipitation / Displacement by Zinc

2Na[Ag(CN)₂] + Zn → Na₂[Zn(CN)₄] + 2Ag

Diagram 11: Cyanide extraction of silver

Chemical Safety Cyanide compounds are acutely toxic. The extraction process is an industrial chemistry topic and requires strict process control, containment and environmental safeguards.

6.3 Silver Chloride — AgCl

Preparation

AgNO₃ + NaCl → AgCl↓ + NaNO₃

AgCl appears as a white curdy precipitate.

Important Property

Silver chloride is photosensitive and darkens on exposure to light because silver is formed:

2AgCl → 2Ag + Cl₂ (light)

Uses

Classical photographic materials and photosensitive chemistry.
Qualitative test/analysis of chloride ions.
Ag/AgCl reference electrodes in electrochemistry.

Diagram 12: Silver chloride formation and photosensitivity

6.4 Silver Nitrate — AgNO₃

Preparation

Silver dissolves in nitric acid. A useful balanced equation with dilute nitric acid is:

3Ag + 4HNO₃(dil.) → 3AgNO₃ + NO + 2H₂O

Properties

Colourless crystalline solid, readily soluble in water.
Provides Ag⁺ ions for precipitation tests.
Light-sensitive and stored in suitable containers.

Ag⁺ + Cl⁻ → AgCl↓

Uses

Analytical reagent for halide ions.
Preparation of other silver compounds.
Specialized laboratory and industrial applications.
Has limited controlled medical uses; it should not be self-applied because concentrated silver nitrate is corrosive.

7. Key Reactions at a Glance

Topic	Important equation	What to remember
Copper self-reduction	2Cu₂O + Cu₂S → 6Cu + SO₂	Produces blister copper
Iron slag	FeO + SiO₂ → FeSiO₃	Removal of iron impurity during copper extraction
Zinc roasting	2ZnS + 3O₂ → 2ZnO + 2SO₂	Converts sulphide to oxide
Zinc reduction	ZnO + C → Zn + CO	Zinc vapour must be condensed
Mercury roasting	HgS + O₂ → Hg + SO₂	Hg vapour condensed
Iron reduction	Fe₂O₃ + 3CO → 2Fe + 3CO₂	Major blast-furnace reduction
Blast-furnace slag	CaO + SiO₂ → CaSiO₃	Limestone supplies CaO flux
Rust anode	Fe → Fe²⁺ + 2e⁻	Iron oxidizes
Rust cathode	O₂ + 2H₂O + 4e⁻ → 4OH⁻	Oxygen reduced in moist neutral conditions
Silver leaching	Ag₂S + 4NaCN ⇌ 2Na[Ag(CN)₂] + Na₂S	Silver becomes soluble complex
Silver recovery	2Na[Ag(CN)₂] + Zn → Na₂[Zn(CN)₄] + 2Ag	Zinc displaces silver
AgCl test	Ag⁺ + Cl⁻ → AgCl↓	White precipitate

8. Important Comparisons

Blue Vitriol vs White Vitriol

Feature	Blue vitriol	White vitriol
Formula	CuSO₄·5H₂O	ZnSO₄·7H₂O
Metal ion	Cu²⁺	Zn²⁺
Appearance	Blue crystals	Colourless/white crystals
With NaOH	Blue Cu(OH)₂ precipitate	White Zn(OH)₂ precipitate; dissolves in excess NaOH

Cu, Zn and Fe Reactivity with Dilute HCl

Metal	Behaviour	Reason / product
Cu	No normal H₂ liberation	Copper lies below hydrogen in common activity series
Zn	Reacts	ZnCl₂ + H₂
Fe	Reacts	FeCl₂ + H₂

Extraction Strategy Comparison

Metal	Ore	Key chemistry
Cu	CuFeS₂	Partial oxidation, slag removal, self-reduction
Zn	ZnS	Roast to ZnO, reduce, condense Zn vapour
Hg	HgS	Roast and condense volatile Hg
Fe	Fe₂O₃	CO reduction in blast furnace
Ag	Ag₂S	Cyanide complex formation and Zn displacement

Diagram 13: Comparison of extraction principles

9. Common Exam Mistakes

Writing CuFeS₂ incorrectly for copper pyrite.
Forgetting that silica removes FeO as FeSiO₃ slag during copper extraction.
Missing the self-reduction equation 2Cu₂O + Cu₂S → 6Cu + SO₂.
Writing Zn metal directly from roasting ZnS. Roasting first gives ZnO; reduction then gives zinc.
Forgetting that zinc produced at high furnace temperature is volatile and must be condensed.
Confusing blue vitriol CuSO₄·5H₂O with white vitriol ZnSO₄·7H₂O.
Confusing calomel Hg₂Cl₂ with corrosive sublimate HgCl₂.
Writing limestone as the reducing agent in the blast furnace. Limestone is the source of CaO flux; CO is the major reducing gas.
Mixing up slag in copper metallurgy (FeSiO₃) with common blast-furnace slag (CaSiO₃).
Describing rusting as a single dry reaction. Moisture and oxygen support an electrochemical corrosion process.
Forgetting zinc in the precipitation step of the silver cyanide process.
Writing AgCl as yellow; silver chloride is characteristically white.
Giving outdated mercury compounds as casual medical recommendations. Their historic uses must be separated from modern safety practice.

10. Exam-Important Reaction Practice

Worked Example 1: Why is Cu unable to liberate H₂ from dilute HCl while Zn can?

Zinc is more readily oxidized than hydrogen in the common activity-series comparison, so:

Zn + 2H⁺ → Zn²⁺ + H₂

Copper is less reactive than hydrogen in this context and therefore does not normally displace H₂ from dilute non-oxidizing acids.

Worked Example 2: Identify the flux and slag in the blast furnace

Limestone decomposes:

CaCO₃ → CaO + CO₂

The product CaO is the basic flux. It reacts with silica gangue:

CaO + SiO₂ → CaSiO₃

Answer: flux-forming material = limestone; active flux = CaO; slag = CaSiO₃.

Worked Example 3: Distinguish blue vitriol and white vitriol

Blue vitriol: CuSO₄·5H₂O, blue hydrated copper(II) sulphate.

White vitriol: ZnSO₄·7H₂O, colourless/white hydrated zinc sulphate.

With NaOH, Cu²⁺ gives a blue Cu(OH)₂ precipitate, while Zn²⁺ gives a white Zn(OH)₂ precipitate that dissolves in excess strong alkali.

Worked Example 4: Silver recovery from cyanide solution

The leached silver exists as the complex ion [Ag(CN)₂]⁻. Zinc is more readily oxidized and displaces Ag:

2Na[Ag(CN)₂] + Zn → Na₂[Zn(CN)₄] + 2Ag

The metallic silver is then collected and refined.

11. Important Exam Questions

Short-Answer Questions

Name the principal ore of copper studied in this unit and write its formula.
What is copper matte?
What is the role of silica in copper extraction?
Write the self-reduction reaction used to obtain copper.
Why is crude copper called blister copper?
What happens when excess aqueous ammonia is added to a Cu²⁺ solution?
Write the formula of blue vitriol, red copper oxide and black copper oxide.
Name the ore of zinc used in this chapter.
Write the roasting reaction of zinc blende.
Show that zinc is amphoteric using one reaction with alkali.
Write the formula of white vitriol.
Name the principal ore of mercury.
Differentiate calomel and corrosive sublimate by formula.
Why is limestone added in the blast furnace?
What is the reducing agent for Fe₂O₃ in the blast furnace?
What is slag? Write the formula of common blast-furnace slag.
State two methods for preventing rusting.
Name the ore of silver commonly used to explain cyanide extraction.
Write the precipitation reaction of AgCl.
Why does AgCl darken in light?

Long-Answer Questions

Describe the extraction of copper from copper pyrite with equations and a flow sheet.
Explain the chemical properties of copper with air, acids, aqueous ammonia and metal ions.
Describe preparation, properties and uses of blue vitriol.
Describe extraction of zinc from zinc blende with equations.
Explain the properties and uses of zinc, including reactions with acid and alkali.
Describe preparation, properties and uses of white vitriol.
Explain occurrence and extraction of mercury from cinnabar.
Describe preparation, properties and uses of calomel and corrosive sublimate.
Describe extraction of iron in a blast furnace with a labelled diagram and equations.
Explain manufacture of steel by the Basic Oxygen Method.
Describe the Open Hearth Process and compare it with the Basic Oxygen Method.
Explain electrochemical corrosion of iron and methods of prevention.
Describe extraction of silver by the cyanide process.
Explain preparation and uses of silver chloride and silver nitrate.

Equation / Conversion Questions

Complete and balance: Cu₂S + O₂ → ?
Complete and balance: Cu₂O + Cu₂S → ?
Complete and balance: ZnS + O₂ → ?
Write the equation showing Zn reacting with NaOH in water.
Write the extraction reaction for Hg from HgS.
Write the equations for formation of CO in the blast furnace.
Write the blast-furnace reduction of Fe₂O₃ by CO.
Write the limestone decomposition and slag-forming reactions.
Write the anodic and cathodic half-reactions involved in rusting.
Write the cyanide leaching and zinc-displacement equations for silver.
Write the reaction for preparation of AgCl from AgNO₃.

Diagram Questions

Draw a flow sheet for extraction of copper from copper pyrite.
Draw a flow sheet for extraction of zinc from zinc blende.
Draw a simple roasting–condensation setup for mercury extraction.
Draw and label the blast furnace.
Draw a Basic Oxygen Furnace and show the oxygen lance and slag layer.
Draw the electrochemical rusting mechanism under a water droplet.
Draw a flow sheet for silver extraction by the cyanide process.
Draw the hydration/dehydration cycle of blue vitriol.

How to score in extraction questions Use a fixed sequence: ore → concentration → chemical conversion → impurity removal → metal recovery → important equations → labelled flow sheet. Do not write only a paragraph when a process diagram can make the answer clearer.

12. One-Minute Revision

Copper ore: CuFeS₂; zinc ore: ZnS; mercury ore: HgS; iron ore commonly used: Fe₂O₃; silver ore: Ag₂S.
Copper extraction removes FeO using SiO₂ to form FeSiO₃ slag.
Copper self-reduction: 2Cu₂O + Cu₂S → 6Cu + SO₂.
Blue vitriol = CuSO₄·5H₂O.
Red copper oxide = Cu₂O; black copper oxide = CuO.
Zinc blende is roasted: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
ZnO is reduced to zinc; hot zinc is collected after condensation.
White vitriol = ZnSO₄·7H₂O.
Mercury is extracted from cinnabar by roasting and condensation.
Calomel = Hg₂Cl₂; corrosive sublimate = HgCl₂.
Blast furnace: CO reduces iron oxide; CaO from limestone removes SiO₂ as CaSiO₃.
BOF makes steel rapidly by blowing oxygen through molten iron.
Rusting needs moisture and oxygen and proceeds electrochemically.
Galvanizing protects iron with zinc.
Silver is extracted by forming soluble [Ag(CN)₂]⁻, then displaced by Zn.
AgCl is a white photosensitive precipitate.
AgNO₃ is an important analytical source of Ag⁺ ions.

13. Diagram Practice

Students should practice these diagrams for the NEB examination:

Unit overview: five metals and their principal ores.
Extraction flow sheet of copper from copper pyrite.
Blue vitriol hydration–dehydration cycle.
Extraction flow sheet of zinc from zinc blende.
Amphoteric behaviour of zinc / zinc hydroxide.
Mercury extraction by roasting and condensation.
Calomel reference electrode.
Blast furnace with charge, hot-air inlet, reduction zone, slag and molten iron.
Basic Oxygen Furnace with oxygen lance.
Electrochemical rusting under a water droplet.
Silver cyanide-process flow sheet.
AgCl precipitation and photochemical decomposition.
Comparison of extraction strategies for Cu, Zn, Hg, Fe and Ag.

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