1. Tardigrade
  2. Question
  3. Chemistry
  4. A1 and A2 are two ores of metal M.A1 on calcination gives black precipitate, CO2 and water. Identify A1 and A2.

Question Error Report

Thank you for reporting, we will resolve it shortly

Back to Question

Q. $A_1$ and $A_2$ are two ores of metal $M.A_1$ on calcination gives black precipitate, $CO_2$ and water.
Identify $A_1$ and $A_2$.Chemistry Question Image

IIT JEEIIT JEE 2004General Principles and Processes of Isolation of Elements

Solution:

$A_1$ is basic copper carbonate $(Cu(OH)_2.CuCO_3)$ while $A_2$ is $Cu_2S.$ The confirmatory reactions are :
(i) $CuCO_3 \cdot Cu(OH)_2\xrightarrow {\Delta} \underset{\text{Black}}{CuO}+CO_2\uparrow+H_2O$
(ii) $CuCO_3 \cdot Cu(OH)_2\xrightarrow {HCl} CuCl_2+CO_2\uparrow+H_2O$
$CuCl_2\xrightarrow {KI} \underset{D}{Cu_2I_2}\downarrow+KCl+I_2$
$A_2\xrightarrow {\text{Roasting}} Cu_2O+SO_2\uparrow$
$Cu_2S+Cu_2O\rightarrow Cu+SO_2\uparrow$
$SO_2$ is a reducing gas that gives green colour with acidified $K_2Cr_2O_7$ as
$3SO_2+K_2Cr_2O_7+H_2SO_4\rightarrow K_2SO_4+ \underset{\text{Green}}{Cr_2(SO_4)_3}+4H_2O$