Isolation of Elements — Advanced Notes & 50 MCQs

1. Ore dressing is performed to:

1. Increase moisture content
2. Remove impurities and concentrate the ore ✅
3. Convert ore into metal directly
4. Reduce particle size only

2. Froth flotation is especially useful for the concentration of:

1. Oxide ores
2. Sulphide ores (e.g., galena, sphalerite) ✅
3. Native metals
4. Highly soluble salts

3. Roasting of sulfide ores primarily converts them to:

1. Hydroxides
2. Oxides (with evolution of SO2) ✅
3. Pure metals directly
4. Carbides

4. Calcination differs from roasting in that calcination is done in absence of:

1. Heat
2. Air/oxygen (calcination is in absence of air) ✅
3. Mineral
4. Reducing agent

5. Ellingham diagrams are plots of:

1. Temperature vs entropy change
2. Temperature vs ΔG° of formation of oxides ✅
3. pH vs solubility
4. Pressure vs volume

6. Which reducing agent is commonly used for the extraction of iron from its oxides in blast furnace?

1. Aluminium powder
2. Carbon (coke) ✅
3. Hydrogen only
4. Electrolysis only

7. Hall–Héroult process is used for industrial extraction of:

1. Iron
2. Aluminium by electrolysis of molten alumina (cryolite) ✅
3. Copper
4. Gold

8. Hydrometallurgy typically involves:

1. High-temperature smelting only
2. Leaching of ores using aqueous solutions ✅
3. Direct mechanical compression
4. Electroplating without dissolution

9. Which of the following metals is refined by electrolytic refining commonly?

1. Iron
2. Copper (anode impure, cathode pure) ✅
3. Aluminium always
4. Magnesium

10. Which method is used to separate a metal from its sulfide ore without converting to oxide?

1. Roasting
2. Smelting after concentration or direct reduction in some cases; hydrometallurgy may be used — generally roasting precedes smelting ✅
3. Cryogenic distillation
4. Zone refining

11. In the extraction of copper from sulphide ores, which step converts Cu2S to Cu?

1. Froth flotation only
2. Smelting and reduction (Cu2S + Fe → Cu + FeS or by roasting) ✅
3. Electrolysis directly from ore
4. Dissolution in water

12. Which of the following is an advantage of hydrometallurgical methods?

1. Always lower operating costs
2. Lower energy requirements and suitability for low-grade ores ✅
3. Always produce no waste
4. Require higher temperatures than pyrometallurgy

13. Which metal is commonly extracted by aluminothermic reduction (thermite process)?

1. Gold
2. Iron from its oxides in special circumstances and production of ferroalloys ✅
3. Mercury
4. Aluminium (itself)

14. Which reagent is used to leach gold from low-grade ores in cyanidation?

1. HCl
2. NaCN (sodium cyanide) in presence of oxygen ✅
3. H2O only
4. NaOH alone

15. Zone refining is primarily used to purify:

1. Bulk iron for construction
2. Semiconductors like silicon and germanium ✅
3. All ores irrespective of composition
4. Aluminium ingots only

16. Which of the following statements about Ellingham diagrams is TRUE?

1. They plot entropy vs pressure
2. They indicate the temperature where oxide formation becomes less favorable and help select reducing agents ✅
3. They are not useful in metallurgy
4. They show solubility limits only

17. Which metal is most commonly obtained by electrolysis of molten chloride rather than oxide?

1. Iron
2. Sodium and other highly reactive metals (e.g., Na from molten NaCl) ✅
3. Copper only
4. Gold from oxide

18. Which process is used to obtain very pure silver from ores or alloys?

1. Hall-Héroult
2. Electrorefining and parting (using HNO3 for gold-silver separation) ✅
3. Thermite exclusively
4. Cyanidation only

19. Which of the following best describes beneficiation?

1. Complete smelting of ore
2. Process of concentrating the ore by removing gangue ✅
3. Electrolytic refining
4. Analytical assay only

20. In the extraction of zinc by roasting and reduction, the intermediate oxide formed is:

1. Zinc carbonate
2. ZnO (zinc oxide) ✅
3. ZnCl2
4. ZnS remains unchanged

21. Which of the following is NOT a method of concentration of ores?

1. Hand picking
2. Winnowing
3. Electrorefining (this is a purification step, not ore concentration) ✅
4. Magnetic separation

22. Silver is often obtained from low-grade ores by which leaching agent?

1. Na2CO3
2. NaCN (cyanidation) often used for Au and Ag ✅
3. H2SO4 only
4. HCl alone

23. In the extraction of aluminium, cryolite is used to:

1. Act as a reducing agent
2. Lower the melting point and improve conductivity of alumina melt ✅
3. Form aluminium-cyanide complexes
4. Separate impurities by flotation

24. Which of these metals is most resistant to extraction by chemical reduction due to its low reactivity?

1. Aluminium
2. Gold (native metal, often recovered by physical methods and refining) ✅
3. Sodium
4. Calcium

25. Which of the following factors does NOT affect choice of extraction method?

1. Reactivity of metal
2. Ore grade and impurities
3. Color of the metal ✅
4. Economic and environmental considerations

26. Direct reduction of iron using natural gas (CO/H2) instead of coke is advantageous because:

1. It always produces pig iron with more impurities
2. It lowers CO2 emissions and can use low-grade ores ✅
3. It increases sulfur content always
4. It requires higher temperatures than blast furnace

27. Which of the following is recovered from roasting sulfide ores to prevent pollution?

1. CO2 gas only
2. SO2, which can be converted to sulfuric acid ✅
3. Pure oxygen
4. Hydrogen gas

28. Which of the following methods concentrates copper ore by utilizing differences in wettability?

1. Magnetic separation
2. Froth flotation (hydrophobic particles attach to bubbles) ✅
3. Electrorefining
4. Smelting only

29. Which process is commonly used for refining of high-purity silicon for electronics?

1. Blast furnace smelting
2. Zone refining and chemical vapor deposition (CVD) ✅
3. Electrolysis of silica
4. Cyanidation

30. Which reagent is used to remove impurities in argentiferous lead during cupellation?

1. Carbon monoxide
2. Air/oxygen oxidizes lead to litharge (PbO) leaving noble metals behind ✅
3. Hydrogen gas only
4. NaCN

31. Which of the following extraction methods would you prefer for a metal with very negative ΔG° of oxide formation?

1. Carbon reduction at low temperature
2. Electrolytic reduction of molten salts ✅
3. Hydrometallurgy with water only
4. Hand picking

32. Which metal is extracted by reduction of its oxide using hydrogen on a commercial scale?

1. Aluminium
2. Tungsten and molybdenum oxides may be reduced by hydrogen in specific processes ✅
3. Copper always
4. Gold

33. Which of the following best describes the purpose of a flux in smelting?

1. Act as reducing agent
2. React with gangue to form fusible slag that can be removed ✅
3. Increase melting point of the charge
4. Produce metal-carbon alloys only

34. Which of the following metals is usually obtained by roasting followed by reduction with carbon?

1. Gold
2. Zinc and lead (from their oxides) ✅
3. Aluminium predominantly
4. Sodium

35. Which of the following statements about electrolytic refining is TRUE?

1. Anode is pure metal and cathode impure
2. Anode is impure, cathode is pure and impurities settle as anode mud ✅
3. It cannot remove dissolved impurities
4. It always consumes the cathode

36. Which metal is extracted by electrochemical reduction of aqueous solution rather than molten salt industrially?

1. Aluminium
2. Copper can be obtained by electrorefining from aqueous solutions ✅
3. Sodium industrially
4. Magnesium from aqueous solution

37. Which of the following techniques is used for removal of sulfur from petroleum fractions?

1. Froth flotation
2. Hydrodesulfurization (catalytic hydrogenation) ✅
3. Blast furnace smelting
4. Zone refining

38. Which of the following is true for native metals?

1. They are bonded ionically in nature
2. Found in nature in elemental form and often recovered by physical methods ✅
3. Always require roasting before extraction
4. Are always radioactive

39. Which of the following is a characteristic of low-grade ore processing?

1. Works only with pyrometallurgy
2. Hydrometallurgy and bioleaching are often suitable for low-grade ores ✅
3. Always economical by smelting
4. Requires zone refining

40. Which of the following is commonly used to purify crude copper to high purity?

1. Fractional distillation
2. Electrolytic refining ✅
3. Leaching with water only
4. Centrifugation only

41. Which of the following is responsible for the liberation of CO2 during calcination of carbonate ores?

1. Oxidation of carbonate
2. Thermal decomposition of carbonate to oxide and CO2 ✅
3. Reduction by hydrogen
4. Dissolution in acids only

42. Which of the following is a common impurity removed during pickle treatment of metals?

1. Organic solvents
2. Oxide scale (using acid cleaning) ✅
3. Diamond inclusions
4. All impurities are left

43. Which of the following is a metallurgical application of magnetic separation?

1. Concentrating paramagnetic iron ores like magnetite ✅
2. Purifying non-magnetic ores only
3. Electrolytic refining directly
4. Removing soluble salts

44. Which of these metals is often recovered by solvent extraction techniques?

1. Iron mostly
2. Copper and uranium (liquid–liquid extraction of metal complexes) ✅
3. Gold by simple filtration
4. Aluminium by flotation

45. Which of the following is an eco-friendly alternative to traditional roasting for sulfide ores?

1. Open roasting with no emission control
2. Bioleaching using microorganisms to oxidize sulfides ✅
3. Thermite process always better
4. None — roasting is the only method

46. Which of the following metals is commonly produced by electrolytic refining to achieve high purity for electrical applications?

1. Iron for structural beams
2. Copper for electrical conductors ✅
3. Lead for batteries only
4. Zinc for roofing only

47. Which extraction route is preferred for metals like titanium which form stable oxides?

1. Carbon reduction at low temp
2. Kroll process (reduction of TiCl4 with Mg) and complex halide routes ✅
3. Electrolysis of oxide in water
4. Simple smelting

48. Which of the following best reduces environmental impact of metal extraction?

1. Ignoring emissions
2. Capture and conversion of SO2, recycling, and using greener leaching agents ✅
3. Increasing roast temperatures always
4. Dumping slag in rivers

49. What is anode mud in electrolytic refining?

1. Pure metal plated on cathode
2. Insoluble impurities that settle at the anode during refining ✅
3. Flux used in smelting
4. Slag only