9.6 Extraction of Metals
Click on any question below to reveal the interactive flashcard answer key:
35. How does a metal's position in the reactivity series relate to the ease of obtaining it from its ore?
Metals low in the series (e.g., copper) hold onto oxygen weakly and are easily reduced via carbon heating. Metals high up (e.g., aluminium) form very stable compounds and require energy-intensive electrolysis to extract.
36. What is the name of the iron ore used in a blast furnace?
Hematite (principally iron(III) oxide, Fe2O3).
37. Describe the initial stage of iron extraction in the blast furnace involving coke.
Coke (carbon) is blasted with hot air and burns exothermically to yield carbon dioxide gas, which provides the high temperatures required for the furnace.
38. How is carbon monoxide produced in the blast furnace?
The rising carbon dioxide gas is reduced by reacting with additional incoming hot coke to form carbon monoxide gas.
39. Describe the reduction of the iron ore in the blast furnace.
Carbon monoxide acts as the main reducing agent, stripping oxygen away from the hematite to form molten iron, which sinks to the bottom of the furnace.
40. What is the purpose of adding limestone (calcium carbonate) to the blast furnace?
It undergoes thermal decomposition to generate calcium oxide, which serves as a basic flux to neutralize acidic sandy impurities (silica) within the furnace.
41. How is slag formed in the blast furnace?
Basic calcium oxide combines with acidic silicon dioxide (silica) impurities to form molten slag (calcium silicate), which floats cleanly on top of the molten iron.
42. State the symbol equation for the burning of coke in the blast furnace.
C(s) + O2(g) → CO2(g)
43. State the symbol equation for the reduction of carbon dioxide to carbon monoxide.
C(s) + CO2(g) → 2CO(g)
44. State the symbol equation for the reduction of iron(III) oxide by carbon monoxide.
Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)
45. State the symbol equation for the thermal decomposition of limestone.
CaCO3(s) → CaO(s) + CO2(g)
46. State the symbol equation for the formation of slag.
CaO(s) + SiO2(s) → CaSiO3(l)
47. What is the main ore of aluminium?
Bauxite (which is purified to yield pure aluminium oxide, Al2O3).
48. By what method is aluminium extracted from its ore?
By the electrolysis of molten aluminium oxide.
49. What is the role of cryolite in the extraction of aluminium?
Cryolite serves as a solvent. It dissolves the aluminium oxide to form an electrolyte with a much lower operating melting point (dropping from roughly 2000°C down to 950°C), significantly reducing energy costs while improving electrical conductivity.
50. Why do the carbon anodes need to be regularly replaced during aluminium extraction?
The oxygen gas liberated at the positive anodes reacts with the carbon blocks at high operational temperatures, producing carbon dioxide gas (C + O2 → CO2) and gradually burning them away.
51. Describe the chemical reactions at the electrodes during the electrolysis of aluminium oxide.
At the negative cathode, aluminium ions gain electrons (reduction):
Al3+ + 3e- → Al
At the positive anode, oxide ions lose electrons (oxidation):
2O2- → O2 + 4e-
Al3+ + 3e- → Al
At the positive anode, oxide ions lose electrons (oxidation):
2O2- → O2 + 4e-