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General Principles And Processes Of Isolation Of Elements

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Question
CBSEENCH12011060
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"Metals are usually not found as nitrates in their ores"
Out of the following two (a and b) reasons which isare/are true for the above observation?
I. Metal nitrates are highly unstable.
II.Metal nitrates are highly soluble in water.

  • I and II are true

  • I and II are false

  • I is false but II is true

  • I is true but II is false

Solution

C.

I is false but II is true

Metals are usually not found as nitrates in their ores, because metal nitrates are highly soluble in water. For example, KNO3 (salt peter) would be classified as completely soluble. Thus, KNO3  could be expected to dissociate completely in aqueous solution into K+ and NO3- ions.
KNO subscript 3 space leftwards harpoon over rightwards harpoon space straight K to the power of plus space left parenthesis aq right parenthesis space plus NO subscript 3 superscript minus space left parenthesis aq right parenthesis
The nitrate anion has three equivalent oxygen surrounding a central nitrogen atom. This tends to spread the single negative charge and make it easier for water to separate the ions in solution.
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Question
CBSEENCH12011395
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Al2O3 can be converted to anhydrous AlCl3 by heating:

  • Al2O3 with HCl gas

  • Al2O3 with NaCl in solid state

  • a mixture of Al2O3 and carbon in dry Cl2 gas

  • Al2O3 with Cl2 gas

Solution

C.

a mixture of Al2O3 and carbon in dry Cl2 gas

Al2O3 may be converted to anhydrous AlCl3 by heating of mixture of Al2O3 and carbon in dry chlorine
Al subscript 2 straight O subscript 3 space plus 3 straight C space plus stack space 3 Cl subscript 2 with Hot space and space dry below space rightwards arrow space stack Al subscript 2 Cl subscript 6 with left parenthesis anhydrous space AlCl subscript 3 right parenthesis below

Question
CBSEENCH12011144
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Aluminium is extracted from alumina (Al2O3) by electrolysis of a molten mixture of 

  • Al2O3 +HF +NaAlF4

  • Al2O3 + CaF2 +NaAlF4

  • Al2O3 +Na3AlF6 +CaF2

  • Al2O3 +KF +Na3AlF6

Solution

C.

Al2O3 +Na3AlF6 +CaF2

Alumina, Al2O3, is a bad conductor of electricity and has a very high melting point, so before subjecting to electrolysis, it is mixed with fluorspar (CaF2) and cryolite (Na3AlF6), which lower its melting point and make it more conducting. 

Question
CBSEENCH12011393
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Copper sulphates dissolves in excess of KCN to give:

  • CuCN

  • [Cu(CN)4]3-

  • [Cu(CN)4]2-

  • Cu(CN)2

Solution

B.

[Cu(CN)4]3-

Copper sulphate on reaction with KCN to give cupric cyanide precipitates firstly which reduce into Cu2CN2 and dissolve in excess of KCN to give soluble K3[Cu(CN)4] complex salt
[CuSO4 + 2KCN →Cu(CN)2 + K2SO4] x 2
2Cu(CN2) → Cu2(CN)2 + NC - CN
Cu2(CN)2 + 6KCN → 2K3[Cu(CN)4]
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2CuSO4 + 10 KCN → 2K3[Cu(CN)4 + 2K2SO4 + (CN)2]

Question
CBSEENCH12011440
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Extraction of gold and silver involves leaching with CN– ion. Silver is later recovered by

  • Liquation

  • Distillation

  • Zone refining

  • Displacement with Zn

Solution

D.

Displacement with Zn

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