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General Principles and processes of Isolation of Elements
easy
The metal extracted by leaching with cyanide is
A
$Cu$
B
$Al$
C
$Na$
D
$Ag$
Solution
Leaching is often used if the ore is soluble in some suitable solvent. In the metallurgy of silver and that of gold, the respective metal is leached with a dilute solution of $NaCN$ or $KCN$ in the presence of air $\left(\right.$ for $\left.O _2\right)$ from which the metal is obtained later by replacement.
$4 M ( s )+8 CN ^{-}( aq )+2 H _2 O ( aq )+ O _2( g ) \rightarrow 4\left[ M ( CN )_2\right]^{-}( aq )+4 OH ^{-}( aq )( M = Ag$ or $Au )$
$2\left[ M ( CN )_2\right]^{-}( aq )+ Zn ( s ) \rightarrow\left[ Zn ( CN )_4\right]^{2-}( aq )+2 M ( s )$
Standard 12
Chemistry
