Question 1(2017)
From the list of terms given, choose the most appropriate term to match the given description:
[calcination, roasting, pulverisation, smelting] -
(i) Crushing of the ore into a fine powder.
(ii) Heating of the ore in the absence of air to a high temperature.
(i) Pulverisation
(ii) Calcination
Key Concepts Covered
This question tests your understanding of the following concepts from the chapter Metallurgy: Question, Terms, Choose, Term, Match, Description. These are fundamental topics in Chemistry that students are expected to master as part of the ICSE Class 10 curriculum.
A thorough understanding of these concepts will help you answer similar questions confidently in your ICSE examinations. These topics are frequently tested in both objective and subjective sections of Chemistry papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This Question
Read the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to Remember
- Balance chemical equations before solving numerical problems.
- Learn the periodic table trends and exceptions.
- Understand reaction mechanisms, not just outcomes.
- Use correct IUPAC nomenclature in your answers.
Practice more questions from Metallurgy — Chemistry, Class 10 ICSE
Chapter Overview: Metallurgy
Metallurgy is the process of extracting metals from their ores and refining them for use. Metals occur in nature as free elements (gold, silver) or combined in ores (oxides, sulphides, carbonates). The extraction process depends on the metal's reactivity: highly reactive metals (Na, Al) are extracted by electrolysis, moderately reactive metals (Fe, Zn) by reduction with carbon, and least reactive metals (Cu, Hg) by simple heating. The general steps include mining, crushing and concentration of ore, extraction (reduction), and refining. Students must understand the extraction of aluminium (electrolysis of alumina in cryolite), iron (blast furnace), and zinc (reduction of ZnO with carbon). The reactivity series determines the method of extraction: metals above carbon require electrolysis; metals below carbon can be reduced by carbon. The chapter also covers alloys (mixtures of metals or metals with non-metals), their composition and uses, and the concept of corrosion and its prevention.
Key Concepts & Reactions
| Term / Process | Details |
|---|---|
| Ore | Mineral from which a metal can be profitably extracted |
| Gangue | Earthy impurities present in the ore |
| Calcination | Heating ore strongly in limited air to remove moisture and CO2 |
| Roasting | Heating ore in excess air to convert sulphides to oxides |
| Smelting | Reduction of metal oxide using carbon or CO in a furnace |
| Flux | Substance added to remove gangue by forming fusible slag |
| Slag | Fusible product of flux + gangue (e.g., CaSiO3) |
| Alloy | Homogeneous mixture of two or more metals (or metal + non-metal) |
Must-Know Concepts
- Blast furnace reactions for iron extraction: Fe2O3 + 3CO → 2Fe + 3CO2
- Coke burns: C + O2 → CO2; then CO2 + C → 2CO (reducing agent)
- Limestone acts as flux: CaCO3 → CaO + CO2; then CaO + SiO2 → CaSiO3 (slag)
- Aluminium extraction: Al2O3 dissolved in cryolite (Na3AlF6), electrolysed at ~950°C
- Common alloys: Brass (Cu + Zn), Bronze (Cu + Sn), Steel (Fe + C), Stainless Steel (Fe + Cr + Ni + C)
- Corrosion prevention: painting, galvanising, electroplating, alloying
Calcination vs Roasting
| Feature | Calcination | Roasting |
|---|---|---|
| Air Supply | Limited or no air | Excess air |
| Ore Type | Carbonates and hydrated ores | Sulphide ores |
| Gas Evolved | CO2 and water vapour | SO2 |
| Example | ZnCO3 → ZnO + CO2 | 2ZnS + 3O2 → 2ZnO + 2SO2 |
Important Diagrams to Practice
- Labelled diagram of the blast furnace with temperature zones and reactions
- Electrolytic cell for aluminium extraction (Hall-Heroult process)
- Flowchart of general metallurgical steps: ore → concentration → extraction → refining
Common Mistakes
- Confusing calcination (limited air, carbonates) with roasting (excess air, sulphides)
- Saying "coke reduces iron oxide" directly (CO is the actual reducing agent, not C)
- Writing wrong alloy compositions (brass is Cu+Zn, NOT Cu+Sn which is bronze)
- Forgetting the role of cryolite in aluminium extraction (lowers melting point)
Scoring Tips
- Draw and label the blast furnace diagram neatly - this is a very common question
- Write balanced equations for each zone of the blast furnace
- Memorise alloy compositions and uses as a table for quick revision
- Link extraction method to position in the reactivity series
Frequently Asked Questions
Why can't aluminium be extracted by carbon reduction?
Aluminium is above carbon in the reactivity series, so carbon cannot reduce Al2O3. Electrolysis of molten alumina (with cryolite) is required to extract aluminium.
What is the role of limestone in the blast furnace?
Limestone (CaCO3) decomposes to CaO, which acts as a flux. It combines with silica (SiO2, the gangue) to form calcium silicate slag (CaSiO3), which floats on molten iron and is removed.
Why are alloys preferred over pure metals?
Alloys are harder, stronger, more resistant to corrosion, and have better properties than pure metals. For example, stainless steel resists rusting unlike pure iron, and brass is harder than pure copper.