Extraction of Metals - Result Question 73
76. $A _1$ and $A _2$ are two ores of metal $M . A _1$ on calcination gives black precipitate, $CO _2$ and water.
Identify $A _1$ and $A _2$.
$(2004,4 M)$
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Solution:
- $A _1$ is basic copper carbonate $\left(Cu(OH) _2 \cdot CuCO _3\right)$ while $A _2$ is $Cu _2 S$. The confirmatory reactions are :
(i) $CuCO _3 \cdot Cu(OH) _2 \xrightarrow{\Delta} CuO+CO _2 \uparrow+H _2 O$
(ii) $CuCO _3 \cdot Cu(OH) _2 \xrightarrow{HCl} CuCl _2+CO _2 \uparrow+H _2 O$
$ \begin{aligned} CuCl _2 \xrightarrow{KI} \underset{D}{Cu _2 I _2 \downarrow}+KCl+I _2 \\ A _2 \xrightarrow{\text { Roasting }} Cu _2 O+SO _2 \uparrow \\ Cu _2 S+Cu _2 O \longrightarrow Cu+SO _2 \uparrow \end{aligned} $
$SO _2$ is a reducing gas that gives green colour with acidified $K _2 Cr _2 O _7$ as
$ 3 \mathrm{SO}_2+\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{K}_2 \mathrm{SO}_4+ \underset{ \text { Green } }{\mathrm{Cr}_2(\mathrm{SO}_4)_3} $ $ +4 \mathrm{H}_2 \mathrm{O} $
BETA
