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General Principles and processes of Isolation of Elements
easy
Leaching of $Ag_2S$ is carried out by heating it with a dilute solution of
A
$NaCN$ only
B
$HCl$
C
$NaOH$
D
$NaCN$ in presence of $O_2$
Solution
Leaching of $Ag _2 S$ is carried out by heating it with a dilute solution of $NaCN$ in presence of $O _2$.
This forms a soluble complex $\left[ Ag ( CN )_2\right]^{-}$.
$Ag _2 S +4 NaCN \rightleftharpoons 4 Na ^{+}+2\left[ Ag ( CN )_2\right]^{2-}+ S ^{2-}$
Here sulphide ion is oxidised to sulphate ion by oxygen.
Thus, soluble material can be separated from insoluble material.
Treatment of the cynaide compound with zinc gives displacement reaction in which silver is obtained.
$2 Na \left[ Ag ( CN )_2\right]+ Zn \rightarrow\left[ Zn ( CN )_4\right]^{2-}+2 Ag \downarrow$
Standard 12
Chemistry
