ICSE Class 10 Chemistry • Chapter 07
| Term | Definition |
|---|---|
| Mineral | Naturally occurring compound of metal found in earth's crust |
| Ore | Mineral from which metal can be extracted profitably |
| Gangue | Earthy impurities associated with ore |
| Metallurgy | Process of extracting metal from its ore |
| Metal | Ore Name | Formula |
|---|---|---|
| Iron | Haematite | Fe₂O₃ |
| Magnetite | Fe₃O₄ | |
| Aluminium | Bauxite | Al₂O₃·2H₂O |
| Zinc | Zinc blende | ZnS |
| Calamine | ZnCO₃ | |
| Copper | Copper pyrites | CuFeS₂ |
Decreasing reactivity (top to bottom):
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au
Memory: "Please Send Charlie's Monkey After Zebras In Large Parks Harbouring Cute Harmless Silver Goldfish"
Extraction Method Based on Activity Series:
| Method | Used For | Principle |
|---|---|---|
| Hydraulic Washing | Heavy ores | Difference in density |
| Magnetic Separation | Magnetic ores (Fe₃O₄) | Magnetic property |
| Froth Flotation | Sulphide ores | Preferential wetting |
Calcination: Heating ore in absence of air (for carbonates)
$ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2$
Roasting: Heating ore in presence of air (for sulphides)
$2ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2$
Reduction with Carbon:
$ZnO + C \xrightarrow{\Delta} Zn + CO$
$Fe_2O_3 + 3CO \xrightarrow{\Delta} 2Fe + 3CO_2$
Electrolytic Reduction: For highly reactive metals (Al)
Purification of metal (e.g., electro-refining for copper)
Ore: Bauxite (Al₂O₃·2H₂O)
Step 1 - Bayer's Process: Purification of bauxite to pure Al₂O₃
Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (dissolution)
NaAlO₂ + 2H₂O → Al(OH)₃ + NaOH (precipitation)
2Al(OH)₃ → Al₂O₃ + 3H₂O (calcination)
Electrolysis of Molten Al₂O₃:
Electrolyte: Al₂O₃ dissolved in molten cryolite (Na₃AlF₆)
Why cryolite? Lowers melting point from 2050°C to 950°C
Cathode: Carbon-lined steel tank
Anode: Graphite rods
At Cathode: Al³⁺ + 3e⁻ → Al
At Anode: 2O²⁻ → O₂ + 4e⁻
Note: Anode gets oxidised by O₂ and needs periodic replacement.
Alloy: A homogeneous mixture of two or more metals, or a metal with non-metal.
Purpose: To improve properties like hardness, strength, corrosion resistance.
| Alloy | Composition | Uses |
|---|---|---|
| Brass | Cu + Zn | Utensils, decorative items |
| Bronze | Cu + Sn | Statues, medals, coins |
| Stainless Steel | Fe + C + Cr + Ni | Surgical instruments, kitchenware |
| Solder | Pb + Sn | Joining electrical wires |
| Duralumin | Al + Cu + Mg + Mn | Aircraft bodies |
| Fuse Metal | Bi + Pb + Sn | Electric fuses |
| Metal Activity | Extraction Method | Example |
|---|---|---|
| High (K, Na, Ca, Mg, Al) | Electrolysis | Al from Al₂O₃ |
| Medium (Zn, Fe, Pb) | Reduction with C/CO | Fe from Fe₂O₃ |
| Low (Cu, Hg, Ag) | Roasting/Heating | Hg from HgS |
BOARD Why is cryolite added during extraction of aluminium? Give electrode reactions.
BOARD Distinguish between calcination and roasting with equations.