chemistry : class12 Leaching : Concentration of ores : General Principles and Processes of Isolation of Elements MCQ Questions and Answers
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Leaching
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MCQ Questions
1. What is leaching in the concentration of ores?
A.
Heating the ore strongly to remove moisture
B.
Selective dissolution of the ore in a suitable solvent
C.
Melting the ore with coke
D.
Grinding the ore into a fine powder
Correct Answer:
Selective dissolution of the ore in a suitable solvent
Explanation:
Leaching is a method in which the ore or its useful component dissolves selectively in a suitable reagent, while the impurities remain undissolved.
2. Which reagent is used for leaching bauxite during the extraction of aluminium?
A.
Sodium hydroxide solution
B.
Hydrochloric acid
C.
Ammonia solution
D.
Sodium chloride solution
Correct Answer:
Sodium hydroxide solution
Explanation:
Bauxite is leached with concentrated sodium hydroxide solution, which dissolves aluminium oxide as soluble sodium aluminate.
3. During the leaching of bauxite, which substance dissolves in sodium hydroxide solution?
A.
Silicon dioxide only
B.
Aluminium oxide
C.
Iron(III) oxide
D.
Calcium carbonate
Correct Answer:
Aluminium oxide
Explanation:
Aluminium oxide in bauxite reacts with sodium hydroxide to form soluble sodium aluminate, allowing aluminium to be separated from many impurities.
4. In the cyanide process, which reagent is used to leach gold from its ore?
A.
Aqueous sodium cyanide
B.
Aqueous sodium carbonate
C.
Dilute sulfuric acid
D.
Aqueous calcium hydroxide
Correct Answer:
Aqueous sodium cyanide
Explanation:
Gold is leached from its ore using an aqueous solution of sodium cyanide in the presence of oxygen, forming a soluble gold cyanide complex.
5. The main purpose of adding air or oxygen during cyanide leaching of gold is to
A.
Cool the ore
B.
Help oxidise gold during complex formation
C.
Remove water from the solution
D.
Convert gold into an insoluble oxide
Correct Answer:
Help oxidise gold during complex formation
Explanation:
Oxygen helps gold dissolve in the cyanide solution by participating in the oxidation process that forms the soluble cyanide complex.
6. Which metal is commonly recovered by leaching its low-grade ore with a dilute acid?
A.
Copper
B.
Sodium
C.
Potassium
D.
Aluminium metal
Correct Answer:
Copper
Explanation:
Low-grade copper ores can be treated by acid leaching, in which copper compounds dissolve in the acid solution and are separated from the gangue.
7. What remains undissolved after the useful component has been removed during leaching?
A.
Gangue or insoluble impurities
B.
Only the pure metal
C.
The solvent
D.
The reducing agent
Correct Answer:
Gangue or insoluble impurities
Explanation:
In leaching, the desired component dissolves in the reagent, whereas insoluble gangue and other impurities remain as residue.
8. Which property is essential for a substance to be separated by leaching?
A.
It must have a different solubility in the selected reagent from the impurities
B.
It must have the highest melting point
C.
It must be magnetic
D.
It must be volatile at room temperature
Correct Answer:
It must have a different solubility in the selected reagent from the impurities
Explanation:
Leaching depends on the selective solubility of the useful ore component or impurity in a suitable solvent.
9. In the Bayer process, the solution obtained after leaching bauxite mainly contains
A.
Sodium aluminate
B.
Iron sulfide
C.
Calcium metal
D.
Copper sulfate
Correct Answer:
Sodium aluminate
Explanation:
Aluminium oxide dissolves in sodium hydroxide during leaching to form soluble sodium aluminate, while insoluble impurities are removed.
10. Which of the following is an example of leaching used in the concentration of an ore?
A.
Dissolving alumina from bauxite in sodium hydroxide
B.
Heating carbonate ore to form its oxide
C.
Reducing a metal oxide with carbon
D.
Melting a metal with another metal
Correct Answer:
Dissolving alumina from bauxite in sodium hydroxide
Explanation:
The dissolution of alumina from bauxite in sodium hydroxide is a standard example of leaching because the useful component is selectively dissolved.
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