chemistry : class12 Bauxite Leaching : Concentration of ores : General Principles and Processes of Isolation of Elements MCQ Questions and Answers
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Bauxite Leaching
MCQ questions and answers.
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MCQ Questions
1. Which process is commonly used for leaching bauxite?
A.
Bayer process
B.
Froth flotation process
C.
Hall-Heroult process
D.
Mond process
Correct Answer:
Bayer process
Explanation:
The Bayer process is used to extract alumina from bauxite by dissolving aluminium oxide in concentrated sodium hydroxide.
2. Which reagent is used to leach aluminium oxide from bauxite in the Bayer process?
A.
Dilute hydrochloric acid
B.
Concentrated sodium hydroxide
C.
Aqueous ammonia
D.
Sodium chloride solution
Correct Answer:
Concentrated sodium hydroxide
Explanation:
Concentrated sodium hydroxide dissolves the amphoteric aluminium oxide present in bauxite, forming soluble sodium aluminate.
3. During the leaching of bauxite, aluminium oxide mainly forms which soluble compound?
A.
Sodium aluminate
B.
Sodium carbonate
C.
Aluminium chloride
D.
Calcium aluminate
Correct Answer:
Sodium aluminate
Explanation:
Aluminium oxide reacts with concentrated sodium hydroxide to form soluble sodium aluminate during bauxite leaching.
4. Which property of aluminium oxide allows it to dissolve in sodium hydroxide during bauxite leaching?
A.
It is acidic only
B.
It is basic only
C.
It is amphoteric
D.
It is neutral
Correct Answer:
It is amphoteric
Explanation:
Aluminium oxide is amphoteric, so it reacts with the base sodium hydroxide and dissolves as soluble sodium aluminate.
5. What is the main insoluble residue left after leaching bauxite with sodium hydroxide?
A.
Red mud
B.
Alumina
C.
Sodium aluminate
D.
Aluminium metal
Correct Answer:
Red mud
Explanation:
Iron oxide and other insoluble impurities remain as a reddish residue called red mud after aluminium oxide dissolves.
6. Which impurity in bauxite generally remains undissolved during treatment with sodium hydroxide?
A.
Aluminium oxide
B.
Iron(III) oxide
C.
Sodium aluminate
D.
Aluminium hydroxide
Correct Answer:
Iron(III) oxide
Explanation:
Iron(III) oxide does not dissolve appreciably in the sodium hydroxide solution and becomes part of the red mud.
7. What is commonly added to the sodium aluminate solution to help precipitate aluminium hydroxide?
A.
Seed crystals of aluminium hydroxide
B.
Pieces of iron
C.
Sodium chloride crystals
D.
Copper powder
Correct Answer:
Seed crystals of aluminium hydroxide
Explanation:
Seeding the sodium aluminate solution with aluminium hydroxide promotes the precipitation of fresh aluminium hydroxide.
8. What precipitates when the sodium aluminate solution is diluted and cooled during the Bayer process?
A.
Aluminium hydroxide
B.
Iron metal
C.
Sodium oxide
D.
Aluminium chloride
Correct Answer:
Aluminium hydroxide
Explanation:
On dilution and cooling, aluminium hydroxide precipitates from the sodium aluminate solution and can be separated.
9. Which compound is obtained by heating the precipitated aluminium hydroxide strongly?
A.
Aluminium oxide
B.
Sodium hydroxide
C.
Iron(III) oxide
D.
Aluminium sulfide
Correct Answer:
Aluminium oxide
Explanation:
Strong heating, or calcination, of aluminium hydroxide removes water and produces aluminium oxide, also called alumina.
10. What is the purpose of leaching in the concentration of bauxite?
A.
To dissolve aluminium oxide selectively
B.
To convert aluminium into metal directly
C.
To dissolve all impurities equally
D.
To convert bauxite into iron oxide
Correct Answer:
To dissolve aluminium oxide selectively
Explanation:
Leaching separates aluminium oxide from insoluble impurities by dissolving it in concentrated sodium hydroxide while leaving much of the gangue behind.
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