Solution - Occurrence of metals Test - p-Block Elements Class 12 Notes | EduRev

Class 12 : Solution - Occurrence of metals Test - p-Block Elements Class 12 Notes | EduRev

 Page 1


CBSE TEST PAPER-01 
CLASS - XII CHEMISTRY (General principles and processes of isolation of elements) 
[Answers] 
Topic: - Occurrence of metals, concentration methods 
Ans.1    The scientific and technological process used for isolation of the metal from its ores is known 
as metallurgy. 
Ans. 2 The earthly or undesired materials which contaminate ore are called gangue. 
Ans. 3 Metal Ore 
Aluminum Bauxite 
Iron  Hematite, Magnetite 
Copper  Copper pyrite, Copper glance 
Zinc  Zinc blende, Calamine 
Ans.4 The most abundant metal is Aluminum & second most abundant metal is iron. 
Ans.5 Benefaction, concentration or dressing of ore means removal of unwanted materials from 
the ore. 
Ans.6 Hydraulic washing is based on the differences in the gravities of the ore and the gangue 
particles. It is used when ore is heavy and impurities are lighter. 
Ans. 7 If either of the ore or gangue is capable of being attracted by a magnetic field e.g. in 
case of iron ores, magnetic separation is used for its concentration. 
Ans. 8 Froth floatation is used for removing 
gangue from sulphide ores. Here a  
suspension of the powdered ore is mixed 
with water. To it collectors and froth  
stabilizer are added. A rotating paddle  
agitates the mixture and draws air in it. 
As a result froth is formed. The mineral  
particles become wet by froth (oil) and gangue particles by water. The froth is skimmed off 
and dried for the recovery of ore.  
Page 2


CBSE TEST PAPER-01 
CLASS - XII CHEMISTRY (General principles and processes of isolation of elements) 
[Answers] 
Topic: - Occurrence of metals, concentration methods 
Ans.1    The scientific and technological process used for isolation of the metal from its ores is known 
as metallurgy. 
Ans. 2 The earthly or undesired materials which contaminate ore are called gangue. 
Ans. 3 Metal Ore 
Aluminum Bauxite 
Iron  Hematite, Magnetite 
Copper  Copper pyrite, Copper glance 
Zinc  Zinc blende, Calamine 
Ans.4 The most abundant metal is Aluminum & second most abundant metal is iron. 
Ans.5 Benefaction, concentration or dressing of ore means removal of unwanted materials from 
the ore. 
Ans.6 Hydraulic washing is based on the differences in the gravities of the ore and the gangue 
particles. It is used when ore is heavy and impurities are lighter. 
Ans. 7 If either of the ore or gangue is capable of being attracted by a magnetic field e.g. in 
case of iron ores, magnetic separation is used for its concentration. 
Ans. 8 Froth floatation is used for removing 
gangue from sulphide ores. Here a  
suspension of the powdered ore is mixed 
with water. To it collectors and froth  
stabilizer are added. A rotating paddle  
agitates the mixture and draws air in it. 
As a result froth is formed. The mineral  
particles become wet by froth (oil) and gangue particles by water. The froth is skimmed off 
and dried for the recovery of ore.  
Ans.9 Depressant adjusts the proportion of oil and water so as to separate two sulphide ores. e.g. in 
case of an ore containing ZnS and PbS, NaCN is used an depressant which selectively 
prevents ZnS from coming to the froth. 
Ans 10.  Pine oil, fatty acids or xanthate can be used as collectors to enhance the non- wettability of 
mineral particles whereas cresols or aniline can be used as froth stabilizer to stabilize the 
froth in froth floatation process. 
Ans 11. Leaching is used if the ore is soluble in suitable solvent. e.g. Aluminum is leached from 
bauxite by using a conc. solution of NaOH at 473-523 K and 35-36 bar pressure. Al
2
O
3
 is 
leached out an sodium aluminates leaving behind impurities- 
Al
2
O
3
 (S) + 2NaOH(aq)+3H
2
O 
4
 2Na[Al(OH) ] ?
The aluminate solution is centralised by passing CO
2
 gas & hydrated Al
2
O
3
 is precipitated 
which is filtered, dried and heated to give pure Al
2
O
3
. 
4 2 2 3 2 3 
2 [ ( ) ] + CO  Al O .xH O(s)+2NaHCO (aq) Na Al OH ? 
1470
2 3 2 2 3 2
. ( ) Al O (s) + xH O (g)
K
Al O xH O S --- ?
Ans.12 A dil. Solution of NaCN or KCN in the presence of air is used as reagent for leaching of 
silver and gold. The equations are- 
2 2 2
4 ( ) 8 ( ) 2 ( ) ( ) 4[M(CN) ] (aq)+4OH (aq) M s CN aq H O aq O g
- - - + + + ? 
(Where M= Ag or Au) 
2
2 4
2[ ( ) ] ( ) ( ) [ ( ) ] ( ) 2 ( ) M CN aq Zn s Zn CN aq M s
- - + ? +
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