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Questions and Answers
Which of the following statements accurately describes the function of sodium hydroxide (NaOH) in Baeyer's process for aluminum extraction?
Which of the following statements accurately describes the function of sodium hydroxide (NaOH) in Baeyer's process for aluminum extraction?
- It acts as a catalyst in the conversion of aluminum hydroxide to pure alumina.
- It reacts selectively with iron(III) oxide ($Fe_2O_3$) to form a soluble complex, thus removing it as an impurity.
- It prevents the precipitation of aluminum hydroxide by maintaining a high pH throughout the process.
- It reacts with the amphoteric bauxite ore to form sodium aluminate, while leaving non-amphoteric impurities unaffected. (correct)
In the context of aluminum extraction, what is the purpose of 'seeding' during the conversion of sodium aluminate ($NaAlO_2$) to aluminum hydroxide ($Al(OH)_3$)?
In the context of aluminum extraction, what is the purpose of 'seeding' during the conversion of sodium aluminate ($NaAlO_2$) to aluminum hydroxide ($Al(OH)_3$)?
- To initiate and accelerate the precipitation of aluminum hydroxide. (correct)
- To control the temperature of the reaction and prevent the formation of unwanted byproducts.
- To neutralize any excess sodium hydroxide present in the solution.
- To remove any remaining iron oxide impurities from the solution.
What distinguishes bauxite from the other listed aluminum ores, cryolite and corundum?
What distinguishes bauxite from the other listed aluminum ores, cryolite and corundum?
- Bauxite contains a higher percentage of aluminum by mass than cryolite or corundum.
- Bauxite is the only ore that can be directly used in the electrolytic refining of aluminum.
- Bauxite is a sodium aluminum fluoride, whereas cryolite and corundum are aluminum oxides.
- Bauxite is a hydrated aluminum oxide, while the others are anhydrous. (correct)
In Hall's process, what is the role of sodium carbonate ($Na_2CO_3$) in the initial stage of dressing the ore?
In Hall's process, what is the role of sodium carbonate ($Na_2CO_3$) in the initial stage of dressing the ore?
Why is the aluminum metal not found in the free state?
Why is the aluminum metal not found in the free state?
During the conversion of sodium aluminate ($NaAlO_2$) to aluminum hydroxide ($Al(OH)_3$), what is the purpose of diluting $NaAlO_2$ with $H_2O$?
During the conversion of sodium aluminate ($NaAlO_2$) to aluminum hydroxide ($Al(OH)_3$), what is the purpose of diluting $NaAlO_2$ with $H_2O$?
In the final step of both Baeyer's and Hall's processes, aluminum hydroxide ($Al(OH)_3$) is heated to produce pure alumina ($Al_2O_3$). What is the primary purpose of this ignition step?
In the final step of both Baeyer's and Hall's processes, aluminum hydroxide ($Al(OH)_3$) is heated to produce pure alumina ($Al_2O_3$). What is the primary purpose of this ignition step?
During Hall's process, after converting bauxite to sodium aluminate ($NaAlO_2$), carbon dioxide ($CO_2$) is introduced. What is the main purpose of this step?
During Hall's process, after converting bauxite to sodium aluminate ($NaAlO_2$), carbon dioxide ($CO_2$) is introduced. What is the main purpose of this step?
Flashcards
Bauxite
Bauxite
Main ore of aluminum, hydrated aluminum oxide.
Cryolite
Cryolite
Sodium aluminum fluoride.
Corundum
Corundum
Alumina oxide.
Baeyer's Process
Baeyer's Process
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Sodium Hydroxide (NaOH)
Sodium Hydroxide (NaOH)
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Hall's Process (dressing ore)
Hall's Process (dressing ore)
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Seeding in purification
Seeding in purification
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Al(OH)3 to Al2O3
Al(OH)3 to Al2O3
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Study Notes
- Aluminium is the most abundant metal in the earth's crust at about 7.4% by mass, followed by iron at 4.7%.
- Aluminium doesn't occur freely due to its reactive nature.
Ores of Aluminium
- Bauxite (Al₂O₃.2H₂O) is the main ore, which is hydrated aluminium oxide.
- Cryolite (Na₃AlF₆) is Sodium aluminium fluoride.
- Corundum (Al₂O₃) is Aluminium oxide.
Dressing the Ore: The Baeyer's Process
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This is the process of concentration of the ore.
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First step is the conversion of Impure Bauxite to Sodium Aluminate.
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Impure bauxite (Al₂O₃.2H₂O) reacts with concentrated NaOH (a base) at 150-200°C to form sodium aluminate (2NaAlO₂) and water (3H₂O).
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NaOH, or caustic alkali, functions as a sodium hydroxide.
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Bauxite is reacted with concentrated solution of NaOH under pressure for two hours.
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This is the first step in obtaining Al₂O₃.
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Impurities like Fe₂O₃ (iron (III) oxide) and SiO₂ present in bauxite remain unaffected by concentrated NaOH because they are not amphoteric.
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Bauxite is amphoteric and reacts with the base, forming sodium aluminate salt and water, separating the impurities out.
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Caustic alkali is added to bauxite ore during purification.
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Second step the conversion of Sodium Aluminate to Aluminium Hydroxide.
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Sodium aluminate (NaAlO₂) reacts with water (2H₂O) at 50-60°C to produce sodium hydroxide (NaOH) and aluminium hydroxide (Al(OH)₃).
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Sodium aluminate is diluted with water, and Al(OH)₃ crystals are added to precipitate out more Al(OH)₃, a process called seeding.
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Insoluble Al(OH)₃ is filtered out and dried after agitation.
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Third step involves the conversion of Al(OH)₃ to pure alumina by heating Al(OH)₃.
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Aluminium hydroxide, 2Al(OH)₃, is heated at 1100°C to produce pure alumina (Al₂O₃) and water vapor (3H₂O).
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Precipitated Al(OH)₃ is ignited to produce pure alumina [Al₂O₃].
Alternative Method: Hall's Process
- Another way of dressing the ore through removal of impurities.
- Impure bauxite is converted into sodium aluminate by heating with sodium carbonate where Al₂O₃.2H₂O + Na₂CO₃ becomes 2NaAlO₂ + 2H₂O + CO₂[g].
- Carbon dioxide is passed into the sodium aluminate solution, resulting in the precipitation of Al(OH)₃ where 2NaAlO₂ + 3H₂O + CO₂ becomes Na₂CO₃ + 2Al(OH)₃↓.
- Dry aluminium hydroxide is ignited at 1100°C to produce pure alumina where 2Al(OH)₃ becomes Al₂O₃ + 3H₂O (vapours).
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Description
Learn about aluminium extraction from bauxite ore using the Baeyer's process. Bauxite is treated with concentrated NaOH to form sodium aluminate, separating aluminium from impurities. This is a crucial initial step in obtaining pure Al₂O₃.
