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Extraction of Fe, Cu, Zn, Al, Ag, Au
JEE Main level
Single correct option
Difficulty 2 of 3
mt133
When argentite,
Ag
X
2
S
, is leached with aqueous
NaCN
it forms
Na
[
Ag
(
CN
)
X
2
]
and
Na
X
2
S
. Air is blown through the mixture mainly to
A
reduce the dicyanidoargentate(I) to silver
B
oxidise
Na
X
2
S
(for example to
Na
X
2
S
X
2
O
X
3
), so that the leaching reaction goes to completion
C
convert sodium cyanide into cyanogen gas
D
precipitate silver as the oxide
Answer: B
Ag
X
2
S
+
4
NaCN
2
Na
[
Ag
(
CN
)
X
2
]
+
Na
X
2
S
is reversible. Dissolved oxygen removes sulphide:
2
Na
X
2
S
+
2
O
X
2
+
H
X
2
O
Na
X
2
S
X
2
O
X
3
+
2
NaOH
, shifting the equilibrium forward.
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