chemistry : class12 Depressants : Concentration of ores : General Principles and Processes of Isolation of Elements MCQ Questions and Answers
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Depressants
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MCQ Questions
1. What is the main function of a depressant in the froth flotation process?
A.
To increase the density of the ore
B.
To selectively prevent certain mineral particles from forming froth
C.
To dissolve the gangue completely
D.
To increase the melting point of the ore
Correct Answer:
To selectively prevent certain mineral particles from forming froth
Explanation:
A depressant selectively prevents a particular mineral from attaching to air bubbles and entering the froth, allowing another mineral to be separated.
2. Which chemical is commonly used as a depressant in the separation of lead sulphide and zinc sulphide ores?
A.
Sodium cyanide
B.
Sodium carbonate
C.
Copper sulphate
D.
Pine oil
Correct Answer:
Sodium cyanide
Explanation:
Sodium cyanide acts as a depressant by preventing zinc sulphide from forming froth during the selective flotation of lead sulphide and zinc sulphide.
3. In the flotation of a mixture of PbS and ZnS, which ore is depressed by adding sodium cyanide?
A.
Lead sulphide
B.
Zinc sulphide
C.
Both lead sulphide and zinc sulphide equally
D.
Neither lead sulphide nor zinc sulphide
Correct Answer:
Zinc sulphide
Explanation:
Sodium cyanide selectively depresses ZnS, while PbS is allowed to attach to air bubbles and rise with the froth.
4. A depressant is added during froth flotation mainly to achieve what?
A.
Selective separation of sulphide ores
B.
Conversion of ore into metal
C.
Removal of all moisture from the ore
D.
Formation of a slag layer
Correct Answer:
Selective separation of sulphide ores
Explanation:
Depressants make one sulphide mineral less likely to enter the froth, helping separate it from another sulphide mineral.
5. When sodium cyanide is added to a mixture of PbS and ZnS in froth flotation, which sulphide preferentially enters the froth?
A.
ZnS
B.
PbS
C.
Both PbS and ZnS equally
D.
Neither PbS nor ZnS
Correct Answer:
PbS
Explanation:
Sodium cyanide depresses ZnS, so PbS remains the sulphide that preferentially attaches to bubbles and enters the froth.
6. What property of a mineral is changed by a depressant during froth flotation?
A.
Its magnetic property only
B.
Its tendency to be wetted and form froth
C.
Its atomic mass
D.
Its nuclear structure
Correct Answer:
Its tendency to be wetted and form froth
Explanation:
A depressant changes the surface behavior of selected mineral particles, reducing their attachment to air bubbles and preventing their flotation.
7. Which statement correctly describes the action of a depressant?
A.
It helps every mineral form froth rapidly
B.
It prevents a selected mineral from being carried into the froth
C.
It converts gangue into a sulphide ore
D.
It increases the quantity of air bubbles permanently
Correct Answer:
It prevents a selected mineral from being carried into the froth
Explanation:
The selective action of a depressant keeps the unwanted mineral in the pulp instead of allowing it to rise with the froth.
8. In selective froth flotation, why is sodium cyanide called a depressant?
A.
Because it increases the frothing of ZnS
B.
Because it suppresses the flotation of ZnS
C.
Because it dissolves all sulphide minerals
D.
Because it acts as the main frothing agent
Correct Answer:
Because it suppresses the flotation of ZnS
Explanation:
Sodium cyanide is termed a depressant because it suppresses the attachment of ZnS particles to air bubbles during separation.
9. Which of the following is an example of selective depression in froth flotation?
A.
Depressing ZnS while allowing PbS to float
B.
Depressing both PbS and ZnS while allowing gangue to float
C.
Making every mineral particle float
D.
Removing only water from the flotation tank
Correct Answer:
Depressing ZnS while allowing PbS to float
Explanation:
Selective depression means preventing one mineral, such as ZnS, from floating while another mineral, such as PbS, is collected in the froth.
10. What would be the effect of adding a suitable depressant to a flotation mixture containing two sulphide ores?
A.
Both ores would necessarily enter the froth together
B.
One selected sulphide ore would remain in the pulp
C.
The ores would change into oxides immediately
D.
The gangue would become the frothing agent
Correct Answer:
One selected sulphide ore would remain in the pulp
Explanation:
A depressant keeps the selected sulphide mineral in the pulp by preventing it from attaching to bubbles, enabling separation from the other sulphide ore.
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