Metallurgy: Detailed Notes

Introduction Metallurgy is the science and technology of metals. It involves the study of their physical and chemical properties, their extraction from ores, their purification, and their preparation for use. Metals are essential materials in various industries, from construction to electronics.

I. Occurrence of Metals

Metals occur in nature in two main forms:

1. Native State: Unreactive metals (e.g., Au, Ag, Pt) are found in their free, uncombined form.
2. Combined State: Most metals are reactive and occur in combined forms as minerals (compounds containing metals) within the Earth’s crust.
   • Ore: A naturally occurring rock or mineral from which a metal can be economically and profitably extracted. All ores are minerals, but all minerals are not ores.
   • Gangue (Matrix): The unwanted rocky or earthy impurities associated with the ore.

Common Types of Ores:

• Oxide Ores: Bauxite (Al2O3.xH2O), Haematite (Fe2O3), Magnetite (Fe3O4), Cassiterite (SnO2), Pyrolusite (MnO2), Zincite (ZnO).
• Sulphide Ores: Galena (PbS), Zinc Blende (ZnS), Cinnabar (HgS), Copper Pyrites (CuFeS2), Argentite (Ag2S).
• Carbonate Ores: Limestone (CaCO3), Calamine (ZnCO3), Malachite (CuCO3.Cu(OH)2), Siderite (FeCO3).
• Halide Ores: Rock Salt (NaCl), Horn Silver (AgCl), Cryolite (Na3AlF6).
• Sulphate Ores: Gypsum (CaSO4.2H2O), Epsom Salt (MgSO4.7H2O), Barytes (BaSO4).

II. Steps Involved in Metallurgy (Extraction of Metals)

The entire process of extracting metals from their ores and refining them is known as metallurgy. It generally involves the following steps:

1. Crushing and Grinding (Pulverization): The ore is first crushed into small pieces in jaw crushers and then finely ground into a powder in ball mills or stamp mills.
2. Concentration of Ore (Benefaction): Removal of unwanted impurities (gangue) from the powdered ore. This step increases the proportion of the metal in the ore. Different methods are used depending on the nature of the ore and gangue:
   • Hydraulic Washing (Gravity Separation): Based on the difference in specific gravities of the ore particles and the gangue. Heavier ore particles settle, while lighter gangue particles are washed away by a stream of water. Used for oxide and carbonate ores (e.g., Haematite, Cassiterite).
   • Magnetic Separation: Used when either the ore or the gangue is magnetic. The powdered ore is passed over a magnetic roller, separating magnetic and non-magnetic components. Used for Chromite (FeCr2O4), Pyrolusite (MnO2), and Tin stone (SnO2 – non-magnetic ore from magnetic gangue).
   • Froth Flotation Method: Used for sulphide ores. Based on the preferential wetting of ore particles by oil (pine oil, eucalyptus oil, fatty acids) and gangue particles by water. The ore particles become lighter and rise to the surface with the froth, while gangue settles. Activators (e.g., CuSO4 for ZnS) and Depressants (e.g., NaCN for ZnS/PbS mixture) are sometimes added.
   • Leaching (Chemical Method): Used when the ore is soluble in a suitable chemical reagent, and the gangue is not. The metal is obtained as a solution, then recovered by precipitation or displacement. Common for Al (Bayer’s process), Au, Ag (MacArthur-Forrest cyanide process).
     • Bayer’s Process for Alumina (from Bauxite): Bauxite is digested with concentrated NaOH solution, forming soluble sodium aluminate. Impurities like Fe2O3 remain insoluble. The solution is diluted and seeded with Al(OH)3, which precipitates. This is then calcined to get pure Al2O3. Al2O3(s) + 2NaOH(aq) + 3H2O(l) → 2NaAl(OH)4 2NaAl(OH)4 → Al2O3.xH2O(s) + 2NaOH(aq) (seeding) 2Al(OH)3(s) → Al2O3(s) + 3H2O(g) (calcination)
     • Cyanide Process for Gold/Silver: Powdered gold/silver ore is leached with a dilute solution of NaCN or KCN in the presence of air. The metal forms a soluble complex. The metal is then recovered by displacement using a more electropositive metal like Zinc. 4Au(s) + 8CN-(aq) + O2(g) + 2H2O(l) → 4[Au(CN)2]-(aq) + 4OH-(aq) 2[Au(CN)2]-(aq) + Zn(s) → [Zn(CN)4]2-(aq) + 2Au(s)
3. Extraction of Crude Metal from Concentrated Ore: This involves converting the concentrated ore into a form suitable for reduction and then reducing it to the crude metal.
   • Calcination: Heating the ore strongly in the absence or limited supply of air, generally below its melting point. Used for carbonate and hydroxide ores to remove volatile impurities and convert them to oxides.
     • ZnCO3(s) → ZnO(s) + CO2(g)
     • Fe2O3.xH2O(s) → Fe2O3(s) + xH2O(g)
   • Roasting: Heating the ore strongly in a regular supply of air, generally below its melting point. Used for sulphide ores to convert them into oxides and remove sulphur as SO2.
     • 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
     • Some sulphide ores are partially roasted to allow self-reduction later (e.g., copper).
   • Reduction of Metal Oxide to Crude Metal: The metal oxide (or other combined form) is then reduced to its metallic form. The choice of reducing agent depends on the metal’s reactivity (position in electrochemical series).
     • Smelting (Carbon Reduction): Used for less reactive metals (Fe, Zn, Cu, Sn). The metal oxide is heated with carbon (coke or charcoal) in a furnace (e.g., blast furnace for iron). Carbon acts as a reducing agent.
       • ZnO(s) + C(s) → Zn(s) + CO(g)
       • Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g) (in blast furnace)
       • Flux: A substance added during smelting to remove non-fusible impurities (acidic gangue needs basic flux like CaO; basic gangue needs acidic flux like SiO2). Flux combines with gangue to form fusible slag.
         • SiO2 (acidic gangue) + CaO (basic flux) → CaSiO3 (slag)
     • Self-Reduction (Auto-Reduction): For some less reactive sulphide ores (Cu, Pb, Hg) that can be partially roasted to form some oxide, which then reacts with the remaining sulphide ore to produce the metal without external reducing agent.
       • 2Cu2S + 3O2 → 2Cu2O + 2SO2
       • 2Cu2O + Cu2S → 6Cu + SO2
     • Aluminothermy (Thermite Process): Used for highly reactive metals like Cr and Mn, whose oxides are difficult to reduce with carbon. Aluminium powder is used as a strong reducing agent.
       • Cr2O3(s) + 2Al(s) → 2Cr(s) + Al2O3(s)
     • Electrolytic Reduction: Used for highly reactive metals (Na, K, Ca, Mg, Al) where chemical reduction is not feasible or economical. The molten metal halide or oxide is electrolysed.
       • Hall-Héroult Process (for Al): Alumina (Al2O3) is dissolved in molten cryolite (Na3AlF6) and electrolysed. Carbon anodes and a graphite-lined steel vessel (cathode) are used.
         • Cathode: Al3+ + 3e- → Al (liquid)
         • Anode: C + O2- → CO + 2e-; C + 2O2- → CO2 + 4e-
     • Hydrometallurgy: Involved in the leaching process, where the metal is obtained from its solution by displacement using a more reactive metal (e.g., Au and Ag extraction).
4. Refining of Crude Metal: The crude metal obtained from the extraction processes often contains impurities. Refining processes are used to obtain the metal in high purity.
   • Distillation: Used for low boiling point metals (Zn, Cd, Hg). The impure metal is heated, vaporized, and then condensed to get the pure metal.
   • Liquation: Used for metals with low melting points (Sn, Pb, Bi) which are much lower than the impurities. The impure metal is heated on a sloping hearth, allowing the pure metal to melt and flow away, leaving the solid impurities behind.
   • Electrolytic Refining: Most widely used and effective method for obtaining high purity metals (Cu, Ag, Au, Zn, Al, Pb, Ni). The impure metal acts as the anode, a thin strip of pure metal as the cathode, and a salt solution of the metal as the electrolyte.
     • Anode (oxidation): Impure Metal → M^n+ + ne- (less reactive metals and impurities settle as anode sludge)
     • Cathode (reduction): M^n+ + ne- → Pure Metal
   • Zone Refining: Used for producing highly pure metals for semiconductors (Ge, Si, Ga, In). Based on the principle that impurities are more soluble in the molten state than in the solid state of the metal. A circular heater moves along a rod of impure metal, creating a molten zone. As the heater moves, impurities move to one end of the rod, which is then cut off.
   • Vapour Phase Refining: The metal is converted into a volatile compound, which is then decomposed to give pure metal.
     • Mond’s Process (for Ni): Impure Nickel is heated with CO to form volatile Ni(CO)4, which is then decomposed at a higher temperature to get pure Ni. Ni(s) + 4CO(g) –(330-350K)–> Ni(CO)4(g) Ni(CO)4(g) –(450-470K)–> Ni(s) + 4CO(g)
     • Van Arkel Method (for Ti, Zr): Impure metal is heated with Iodine to form a volatile iodide, which is then decomposed on a hot tungsten filament. Zr(s) + 2I2(g) –(870K)–> ZrI4(g) ZrI4(g) –(2075K)–> Zr(s) + 2I2(g)
   • Chromatographic Methods: Used for ultra-purification, especially when components are available in minute quantities or impurities have similar chemical properties to the main element. (e.g., Ion-exchange chromatography, gas chromatography).

III. Thermodynamics of Metallurgy (Ellingham Diagrams)

• Ellingham Diagram: A graph plotting ΔG° (Gibbs free energy change) for the formation of metal oxides against temperature. It helps predict the feasibility of a reduction reaction and the choice of reducing agent.
  • A reaction is feasible if ΔG° is negative.
  • The lower a line is on the diagram, the more stable the oxide is.
  • A reducing agent (e.g., C) can reduce a metal oxide if its own oxidation line (e.g., C to CO or CO2) lies below the metal oxide formation line at that temperature.
  • The intersection point of two lines indicates the temperature at which both reactions have the same ΔG°. Above this temperature, the substance with the lower line can reduce the oxide of the substance with the higher line.
  • Slope of lines: Changes with the change in entropy (ΔS°).
    • M(s) + O2(g) → MO2(s): ΔS° is negative (gas to solid), so slope is positive.
    • C(s) + 1/2 O2(g) → CO(g): ΔS° is positive (solid to gas), so slope is negative (or slightly positive but less steep).
    • 2CO(g) + O2(g) → 2CO2(g): ΔS° is negative.
  • Key Inference: Carbon monoxide (CO) is a better reducing agent for Fe2O3 at lower temperatures, while carbon (C) is a better reducing agent at higher temperatures.

IV. Specific Metal Extractions

A. Extraction of Iron (from Haematite ore, Fe2O3) – Blast Furnace

• Raw Materials: Concentrated ore (Haematite), Coke (reducing agent and fuel), Limestone (flux).
• Reactions in Blast Furnace:
  • Zone of Combustion (bottom, 2000K): Coke burns, producing CO2. Heat is generated. C(s) + O2(g) → CO2(g) (exothermic)
  • Zone of Reduction (top, 500-800K): CO2 reacts with coke to form CO (reducing agent). Fe2O3 is reduced by CO. CO2(g) + C(s) → 2CO(g) 3Fe2O3 + CO → 2Fe3O4 + CO2 Fe3O4 + 4CO → 3Fe + 4CO2 Fe2O3 + 3CO → 2Fe + 3CO2
  • Zone of Slag Formation (middle, 1200K): Limestone decomposes to CaO, which acts as a basic flux to remove acidic impurities like SiO2. CaCO3(s) → CaO(s) + CO2(g) CaO(s) + SiO2(s) → CaSiO3(l) (slag)
  • Zone of Fusion (middle, 1500K): Molten iron collects at the bottom, and molten slag floats on top.
• Products:
  • Pig Iron: Crude iron (about 4% carbon and other impurities). Hard and brittle.
  • Slag: CaSiO3, used in road construction and cement.
  • Waste gases: CO, CO2, N2.

B. Extraction of Copper (from Copper Pyrites, CuFeS2)

• Crushing and Concentration: Froth flotation.
• Roasting: Sulphide ore is roasted in a reverberatory furnace. Some sulphur and arsenic impurities are removed. CuFeS2 converts to Cu2S, FeS, and some oxides. 2CuFeS2 + O2 → Cu2S + 2FeS + SO2
• Smelting (in Reverberatory Furnace): Roasted ore is mixed with silica (flux) and heated. FeS is oxidized to FeO, which reacts with SiO2 to form FeSiO3 (slag). Cu2S (matte) is formed. FeO + SiO2 → FeSiO3 (slag)
• Bessemerisation (in Bessemer Converter): Molten matte (Cu2S and residual FeS) is transferred to a Bessemer converter. Air blast is passed through. FeS is oxidized and removed as slag. Cu2S undergoes self-reduction. 2FeS + 3O2 → 2FeO + 2SO2 FeO + SiO2 → FeSiO3 (slag) 2Cu2S + 3O2 → 2Cu2O + 2SO2 2Cu2O + Cu2S → 6Cu + SO2 (Blister Copper)
• Refining: Blister copper (98% pure, due to SO2 bubbles) is refined by electrolytic refining.

C. Extraction of Zinc (from Zinc Blende, ZnS or Calamine, ZnCO3)

• Concentration: Froth flotation for ZnS.
• Roasting (for ZnS) or Calcination (for ZnCO3): Converts to ZnO. 2ZnS + 3O2 → 2ZnO + 2SO2 ZnCO3 → ZnO + CO2
• Reduction (Smelting): ZnO is mixed with coke and heated to 1673 K in vertical retorts. Zinc vaporizes and is condensed (Spelter). ZnO + C → Zn + CO
• Refining: Distillation (for crude zinc), or electrolytic refining for higher purity.

V. Alloys

An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, prepared by melting the components together. Alloys are generally stronger, more corrosion-resistant, and have better properties than their constituent pure metals.

Examples:

• Brass: Cu + Zn
• Bronze: Cu + Sn
• Stainless Steel: Fe + Cr + Ni + C (low)
• Duralumin: Al + Cu + Mg + Mn
• Solder: Pb + Sn
• Amalgam: Any alloy of mercury with another metal (e.g., Dental amalgam: Ag-Sn-Hg alloy).

VI. Corrosion

Corrosion is the process of deterioration of a metal as a result of its reaction with the environment. It is an electrochemical process.

• Rusting of Iron: The most common example of corrosion. Iron reacts with oxygen and water to form hydrated ferric oxide (Fe2O3.xH2O), which is commonly known as rust.
  • Anode (Fe is oxidized): Fe(s) → Fe^2+(aq) + 2e-
  • Cathode (O2 is reduced in presence of H+ from water/CO2): O2(g) + 4H+(aq) + 4e- → 2H2O(l)
  • Overall: 2Fe(s) + O2(g) + 4H+(aq) → 2Fe^2+(aq) + 2H2O(l)
  • Fe^2+ is further oxidized by atmospheric oxygen to Fe^3+, which forms hydrated ferric oxide (rust). 2Fe^2+(aq) + 1/2 O2(g) + 2H2O(l) → Fe2O3.H2O(s) (rust) + 4H+(aq)

Methods of Preventing Corrosion:

• Barrier Protection: Painting, oiling, greasing, plastic coating.
• Sacrificial Protection: Connecting the metal to a more electropositive metal (e.g., galvanization – coating iron with zinc). Zinc corrodes preferentially, protecting iron.
• Electrochemical Protection (Cathodic Protection): Supplying electrons to the metal by connecting it to a more reactive metal (sacrificial anode) or an external power source.
• Alloying: Making alloys (e.g., stainless steel is more resistant than pure iron).
• Anti-rust solutions: Phosphates or chromates form a protective layer.

50 Important MCQs on Metallurgy

1. Which of the following metals is found in the native state? (a) Iron (b) Aluminum (c) Gold (d) Zinc
2. The unwanted earthy or rocky materials associated with an ore are called: (a) Flux (b) Slag (c) Gangue (d) Mineral
3. Froth flotation method is generally used for the concentration of: (a) Oxide ores (b) Sulphide ores (c) Carbonate ores (d) Halide ores
4. Which of the following processes is used for the concentration of bauxite ore? (a) Magnetic separation (b) Froth flotation (c) Leaching (d) Hydraulic washing
5. The role of a depressant in froth flotation process is to: (a) Stabilize the froth (b) Selectively prevent one sulphide ore from coming with the froth (c) Enhance the floatability of the ore (d) Remove gangue by gravity
6. Calcination is the process of heating an ore in: (a) Excess air (b) Limited supply of air (c) Absence of air (d) Presence of a reducing agent
7. Roasting is generally carried out for which type of ores? (a) Carbonate ores (b) Sulphate ores (c) Sulphide ores (d) Oxide ores
8. The main purpose of smelting is to: (a) Concentrate the ore (b) Convert ore to oxide (c) Reduce the metal oxide to metal (d) Refine the crude metal
9. Which of the following reducing agents is used in the blast furnace for the extraction of iron? (a) Aluminum (b) Carbon (Coke) (c) Carbon Monoxide (CO) (d) Both (b) and (c)
10. The flux used in the extraction of iron from haematite ore is: (a) Silica (b) Limestone (c) Borax (d) Cryolite
11. What is “slag” in metallurgical processes? (a) The pure metal obtained (b) The unwanted impurities removed from the ore (c) A fusible product formed by the reaction of flux with gangue (d) A reducing agent
12. The Hall-Héroult process is used for the extraction of: (a) Iron (b) Copper (c) Zinc (d) Aluminum
13. In the electrolytic refining of copper, the anode is made of: (a) Pure copper (b) Impure copper (c) Graphite (d) Platinum
14. Zone refining method is based on the principle that: (a) Impurities are more soluble in the solid state than in the molten state of the metal (b) Impurities are more soluble in the molten state than in the solid state of the metal (c) Metals have different boiling points (d) Metals have different densities
15. Mond’s process is used for the refining of: (a) Titanium (b) Zirconium (c) Nickel (d) Silver
16. Which of the following metals is refined by Van Arkel method? (a) Copper (b) Zinc (c) Titanium (d) Iron
17. An Ellingham diagram plots: (a) ΔH° vs T (b) ΔS° vs T (c) ΔG° vs T (d) Keq vs T
18. In an Ellingham diagram, a metal oxide can be reduced by a reducing agent if the line for the formation of the reducing agent’s oxide lies: (a) Above the metal oxide line (b) Below the metal oxide line (c) Parallel to the metal oxide line (d) Intersects the metal oxide line at a very low temperature
19. Which of the following is considered a better reducing agent for Fe2O3 at higher temperatures in a blast furnace? (a) CO (b) C (c) H2 (d) Al
20. Blister copper is obtained from: (a) Smelting of roasted copper ore (b) Electrolytic refining of copper (c) Bessemerisation of copper matte (d) Calcination of malachite
21. The main impurity present in pig iron is: (a) Silicon (b) Manganese (c) Phosphorus (d) Carbon
22. Galvanization is a method of preventing rust by coating iron with: (a) Tin (b) Chromium (c) Zinc (d) Nickel
23. Which of the following alloys contains mercury? (a) Brass (b) Bronze (c) Solder (d) Amalgam
24. The chemical formula of rust is: (a) FeO (b) Fe2O3 (c) Fe2O3.xH2O (d) Fe3O4
25. Corrosion is essentially a/an: (a) Physical process (b) Chemical process (c) Electrochemical process (d) Biological process
26. Which method is most suitable for refining low boiling metals like Zinc and Mercury? (a) Liquation (b) Distillation (c) Electrolytic refining (d) Zone refining
27. The role of cryolite in the Hall-Héroult process is to: (a) Act as a flux (b) Lower the melting point of alumina (c) Increase the conductivity of the electrolyte (d) Both (b) and (c)
28. In the cyanide process for the extraction of gold, the reducing agent used to precipitate gold from the complex is: (a) Carbon (b) Hydrogen (c) Zinc (d) Aluminum
29. Copper matte contains: (a) Cu2O and FeO (b) Cu2S and FeS (c) CuS and FeS (d) Cu and Fe
30. Which of the following statements is true about an ore? (a) All minerals are ores. (b) All ores are minerals. (c) Ores are always pure compounds. (d) Ores are found only in the native state.
31. The primary purpose of concentration of ore is to: (a) Convert the ore into metal (b) Remove volatile impurities (c) Increase the percentage of metal in the ore (d) Prepare the ore for electrolytic refining
32. Which of the following is an example of an oxide ore? (a) Galena (b) Zinc blende (c) Cinnabar (d) Haematite
33. Which method is based on the principle of difference in specific gravities? (a) Froth flotation (b) Magnetic separation (c) Hydraulic washing (d) Leaching
34. Self-reduction process is used for the extraction of metals like: (a) Al and Mg (b) Fe and Zn (c) Cu and Pb (d) Na and K
35. The Bessemer converter is used in the metallurgy of: (a) Aluminum (b) Iron (c) Copper (d) Zinc
36. Which of the following is not a method of preventing corrosion? (a) Alloying (b) Annealing (c) Galvanization (d) Cathodic protection
37. The metal that is extracted by electrolytic reduction of its molten chloride is: (a) Aluminum (b) Copper (c) Sodium (d) Iron
38. The process of converting hydrated alumina into anhydrous alumina is called: (a) Roasting (b) Calcination (c) Smelting (d) Leaching
39. Stainless steel is an alloy of iron with: (a) Carbon and Tin (b) Chromium and Nickel (c) Zinc and Copper (d) Aluminum and Manganese
40. In the Ellingham diagram, the line with a negative slope typically represents the formation of an oxide where: (a) A solid reacts with a gas to form a solid (b) A solid reacts with a gas to form a gas (c) A liquid reacts with a gas to form a solid (d) A gas reacts with a gas to form a liquid
41. Which zone in the blast furnace is responsible for the formation of slag? (a) Zone of combustion (b) Zone of reduction (c) Zone of slag formation (d) Zone of fusion
42. What is the approximate carbon content in pig iron? (a) Less than 0.2% (b) 0.2% to 2% (c) Around 4% (d) Greater than 5%
43. Which of the following is a common flux for acidic impurities? (a) SiO2 (b) CaO (c) Al2O3 (d) FeO
44. Which process involves the formation of a volatile complex that is later decomposed? (a) Zone refining (b) Electrolytic refining (c) Vapour phase refining (d) Liquation
45. The ore Cinnabar (HgS) is concentrated by: (a) Magnetic separation (b) Froth flotation (c) Leaching (d) Hydraulic washing
46. In the electrolytic refining of copper, the impurities like Au, Ag, Pt settle down as: (a) Cathode sludge (b) Anode sludge (c) Electrolytic impurities (d) Slag
47. Thermite process is a type of: (a) Carbon reduction (b) Electrolytic reduction (c) Aluminothermy (d) Self-reduction
48. Which alloy is primarily used for soldering? (a) Brass (b) Bronze (c) Solder (d) Duralumin
49. What is the primary reducing agent in the upper part of the blast furnace? (a) Coke (b) Carbon monoxide (c) Hydrogen (d) Iron
50. The method used for obtaining ultra-pure silicon for semiconductors is: (a) Liquation (b) Distillation (c) Zone refining (d) Electrolytic refining

Answer Key and Explanations for Metallurgy MCQs

1. Which of the following metals is found in the native state? (c) Gold
   • Explanation: Gold, silver, and platinum are unreactive metals and are often found in their uncombined (native) state in nature.
2. The unwanted earthy or rocky materials associated with an ore are called: (c) Gangue
   • Explanation: Gangue, also known as matrix, refers to the undesirable impurities present in an ore.
3. Froth flotation method is generally used for the concentration of: (b) Sulphide ores
   • Explanation: This method relies on the preferential wetting of sulphide ore particles by oil, causing them to float as froth, while the gangue settles in water.
4. Which of the following processes is used for the concentration of bauxite ore? (c) Leaching
   • Explanation: Bauxite (an aluminum oxide ore) is concentrated using chemical methods like the Bayer’s process, which is a type of leaching.
5. The role of a depressant in froth flotation process is to: (b) Selectively prevent one sulphide ore from coming with the froth
   • Explanation: Depressants are used in the froth flotation process to prevent certain sulphide minerals from forming froth with the desired mineral. For example, NaCN is used as a depressant to separate ZnS from PbS.
6. Calcination is the process of heating an ore in: (c) Absence of air
   • Explanation: Calcination involves heating the ore strongly below its melting point in the absence or limited supply of air to remove volatile matter (e.g., CO2 from carbonates, H2O from hydroxides).
7. Roasting is generally carried out for which type of ores? (c) Sulphide ores
   • Explanation: Roasting involves heating the ore in a regular supply of air, typically for sulphide ores, to convert them into oxides and remove sulphur dioxide.
8. The main purpose of smelting is to: (c) Reduce the metal oxide to metal
   • Explanation: Smelting is a pyrometallurgical process where the concentrated ore (usually oxide) is heated with a reducing agent (like carbon) to extract the crude metal.
9. Which of the following reducing agents is used in the blast furnace for the extraction of iron? (d) Both (b) and (c)
   • Explanation: In the blast furnace, coke (carbon) acts as a primary reducing agent at high temperatures, while carbon monoxide (formed from coke) acts as the main reducing agent in the upper, cooler regions.
10. The flux used in the extraction of iron from haematite ore is: (b) Limestone
    • Explanation: Limestone (CaCO3) decomposes to CaO, which acts as a basic flux to remove acidic impurities (like SiO2) present in haematite ore, forming slag (CaSiO3).
11. What is “slag” in metallurgical processes? (c) A fusible product formed by the reaction of flux with gangue
    • Explanation: Slag is the molten, fusible material formed when flux combines with gangue during smelting. It separates from the molten metal.
12. The Hall-Héroult process is used for the extraction of: (d) Aluminum
    • Explanation: This is the primary industrial method for the electrolytic reduction of alumina (Al2O3) to produce aluminum metal.
13. In the electrolytic refining of copper, the anode is made of: (b) Impure copper
    • Explanation: In electrolytic refining, the impure metal acts as the anode, where it gets oxidized, and the metal ions then move to the cathode to be reduced and deposited as pure metal.
14. Zone refining method is based on the principle that: (b) Impurities are more soluble in the molten state than in the solid state of the metal
    • Explanation: As a molten zone moves along a metal rod, impurities preferentially dissolve in the molten part and are swept to one end, leaving behind a highly pure metal.
15. Mond’s process is used for the refining of: (c) Nickel
    • Explanation: Mond’s process involves converting impure nickel into volatile nickel tetracarbonyl, which is then decomposed to yield pure nickel.
16. Which of the following metals is refined by Van Arkel method? (c) Titanium
    • Explanation: The Van Arkel method (or iodide process) is used for refining highly reactive metals like titanium and zirconium by forming a volatile iodide and then decomposing it.
17. An Ellingham diagram plots: (c) ΔG° vs T
    • Explanation: Ellingham diagrams show the Gibbs free energy change (ΔG°) for the formation of various metal oxides as a function of temperature (T).
18. In an Ellingham diagram, a metal oxide can be reduced by a reducing agent if the line for the formation of the reducing agent’s oxide lies: (b) Below the metal oxide line
    • Explanation: For a reduction to be spontaneous, the overall ΔG° of the coupled reaction must be negative. This happens when the reducing agent’s oxidation reaction has a more negative (or less positive) ΔG° compared to the metal oxide’s formation at that temperature. Graphically, this means its line is below the metal oxide line.
19. Which of the following is considered a better reducing agent for Fe2O3 at higher temperatures in a blast furnace? (b) C
    • Explanation: On an Ellingham diagram for iron, the line for C to CO has a negative slope, meaning its reducing power increases with temperature. At higher temperatures, carbon (coke) becomes a more effective reducing agent than carbon monoxide.
20. Blister copper is obtained from: (c) Bessemerisation of copper matte
    • Explanation: Blister copper (98% pure) is obtained after the Bessemerisation process due to the escaping SO2 gas, which creates a blistered appearance.
21. The main impurity present in pig iron is: (d) Carbon
    • Explanation: Pig iron is crude iron containing about 4% carbon, along with other impurities like Si, Mn, P, S.
22. Galvanization is a method of preventing rust by coating iron with: (c) Zinc
    • Explanation: Galvanization provides sacrificial protection; zinc is more reactive than iron and corrodes preferentially, protecting the iron.
23. Which of the following alloys contains mercury? (d) Amalgam
    • Explanation: An amalgam is an alloy of mercury with another metal or metals. Dental amalgam is a common example.
24. The chemical formula of rust is: (c) Fe2O3.xH2O
    • Explanation: Rust is hydrated ferric oxide, meaning its exact water content (x) can vary.
25. Corrosion is essentially a/an: (c) Electrochemical process
    • Explanation: Corrosion involves redox reactions, where the metal acts as an anode and undergoes oxidation, while a cathodic reaction (usually reduction of oxygen) occurs.
26. Which method is most suitable for refining low boiling metals like Zinc and Mercury? (b) Distillation
    • Explanation: Metals with low boiling points can be easily vaporized and then condensed to obtain a pure form, making distillation a suitable refining method.
27. The role of cryolite in the Hall-Héroult process is to: (d) Both (b) and (c)
    • Explanation: Cryolite (Na3AlF6) acts as a solvent for alumina, significantly lowering its melting point from over 2000°C to about 950°C, and it also increases the electrical conductivity of the electrolyte.
28. In the cyanide process for the extraction of gold, the reducing agent used to precipitate gold from the complex is: (c) Zinc
    • Explanation: After gold forms a soluble cyanide complex ([Au(CN)2]-), zinc is used to displace gold due to its higher reactivity (electropositivity).
29. Copper matte contains: (b) Cu2S and FeS
    • Explanation: Copper matte is the molten mixture obtained after smelting roasted copper pyrites, primarily consisting of cuprous sulphide (Cu2S) and ferrous sulphide (FeS).
30. Which of the following statements is true about an ore? (b) All ores are minerals.
    • Explanation: A mineral is a naturally occurring solid, inorganic substance with a definite chemical composition and crystal structure. An ore is a mineral (or rock) from which a metal can be extracted economically. Thus, all ores are minerals, but not all minerals are ores.
31. The primary purpose of concentration of ore is to: (c) Increase the percentage of metal in the ore
    • Explanation: Concentration (or beneficiation) aims to remove gangue, thereby increasing the proportion of the desired metal compound in the ore, making subsequent extraction steps more efficient.
32. Which of the following is an example of an oxide ore? (d) Haematite
    • Explanation: Haematite (Fe2O3) is a major iron oxide ore. Galena (PbS), Zinc blende (ZnS), and Cinnabar (HgS) are sulphide ores.
33. Which method is based on the principle of difference in specific gravities? (c) Hydraulic washing
    • Explanation: Hydraulic washing (or gravity separation) is effective for ores where the ore particles are significantly denser than the gangue, allowing separation by washing with water.
34. Self-reduction process is used for the extraction of metals like: (c) Cu and Pb
    • Explanation: Copper (from Cu2S) and Lead (from PbS) can undergo self-reduction where a part of the sulphide ore is roasted to oxide, which then reacts with the remaining sulphide to produce the metal.
35. The Bessemer converter is used in the metallurgy of: (c) Copper
    • Explanation: The Bessemer converter is used in the Bessemerisation process to convert copper matte into blister copper.
36. Which of the following is not a method of preventing corrosion? (b) Annealing
    • Explanation: Annealing is a heat treatment process used to make metals softer and more ductile, it does not directly prevent corrosion. Alloying, galvanization, and cathodic protection are common methods for corrosion prevention.
37. The metal that is extracted by electrolytic reduction of its molten chloride is: (c) Sodium
    • Explanation: Highly reactive metals like sodium (from molten NaCl) and magnesium (from molten MgCl2) are extracted by the electrolytic reduction of their fused chlorides. Aluminum is extracted from its oxide dissolved in cryolite.
38. The process of converting hydrated alumina into anhydrous alumina is called: (b) Calcination
    • Explanation: Hydrated alumina (Al2O3.xH2O or Al(OH)3) is heated strongly (calcined) to drive off water and obtain anhydrous alumina (Al2O3).
39. Stainless steel is an alloy of iron with: (b) Chromium and Nickel
    • Explanation: Stainless steel is an iron-based alloy primarily containing chromium (for corrosion resistance) and nickel (for ductility and strength), along with a low percentage of carbon.
40. In the Ellingham diagram, the line with a negative slope typically represents the formation of an oxide where: (b) A solid reacts with a gas to form a gas
    • Explanation: For reactions like C(s) + 1/2 O2(g) -> CO(g), there is an increase in the number of gaseous moles (1/2 mole of gas consumed, 1 mole of gas produced). This positive change in entropy (ΔS > 0) makes the slope of the ΔG vs T line negative (since ΔG = ΔH – TΔS).
41. Which zone in the blast furnace is responsible for the formation of slag? (c) Zone of slag formation
    • Explanation: This zone, typically in the middle part of the blast furnace, is where limestone decomposes and reacts with acidic impurities to form molten slag.
42. What is the approximate carbon content in pig iron? (c) Around 4%
    • Explanation: Pig iron is crude iron containing a high percentage of carbon (typically 3-5%) along with other impurities.
43. Which of the following is a common flux for acidic impurities? (b) CaO
    • Explanation: Calcium oxide (CaO), derived from limestone, is a basic flux used to remove acidic impurities like silica (SiO2) by forming calcium silicate slag.
44. Which process involves the formation of a volatile complex that is later decomposed? (c) Vapour phase refining
    • Explanation: Vapour phase refining methods like Mond’s process (for Ni) and Van Arkel method (for Ti, Zr) rely on forming a volatile compound of the metal, purifying it, and then decomposing it to obtain the pure metal.
45. The ore Cinnabar (HgS) is concentrated by: (b) Froth flotation
    • Explanation: Cinnabar is a sulphide ore, and froth flotation is the most suitable method for concentrating sulphide ores.
46. In the electrolytic refining of copper, the impurities like Au, Ag, Pt settle down as: (b) Anode sludge
    • Explanation: During electrolytic refining, less reactive metals (like Au, Ag, Pt) present in the impure anode do not get oxidized and fall to the bottom as anode sludge.
47. Thermite process is a type of: (c) Aluminothermy
    • Explanation: The thermite process uses aluminum powder as a reducing agent to extract metals from their oxides (e.g., Cr from Cr2O3), hence it’s a type of aluminothermy.
48. Which alloy is primarily used for soldering? (c) Solder
    • Explanation: Solder is a low-melting point alloy, typically of lead and tin, used to join metal workpieces.
49. What is the primary reducing agent in the upper part of the blast furnace? (b) Carbon monoxide
    • Explanation: In the cooler upper regions of the blast furnace, carbon monoxide (CO) is the predominant reducing agent for iron oxides. At higher temperatures, coke (C) takes over.
50. The method used for obtaining ultra-pure silicon for semiconductors is: (c) Zone refining
    • Explanation: Zone refining is specifically employed to achieve extremely high purity metals, which is crucial for semiconductor applications like silicon and germanium.