Question

A1 and A2 are two ores of metal M. A1 on calcination gives black precipitate, CO2 and water, and A2 forms a green-coloured complex with acidified K2Cr2O7. 

A1 and A2 respectively are

• (A) CuCO3.Cu(OH)2 and Cu2S
• (B) Cu2S and CuCO3.Cu(OH)2
• (C) CuCO3 and Cu2S
• (D) CuO and CuCO3

Answer 1

The Correct Option is A

Explanation:
$A_1$ will be malachite, $i.e.{\mathrm{CuCO}}_3\cdot \mathrm{Cu}(\mathrm{OH}{)}_2$$A_2$ will be copper glance, i.e. ${\mathrm{Cu}}_2\mathrm{S}$The confirmatory reactions are as follows:(a) For Malachite(i) ${\mathrm{CuCO}}_3\cdot \mathrm{Cu}(\mathrm{OH}{)}_2-\frac{\text{ Calanation }}{⟶}\underset{\text{bladk solid }}{\underbrace{2{\mathrm{Cu}}_{\mathrm{UO}}}}+{\mathrm{CO}}_2\uparrow +{\mathrm{H}}_2\mathrm{O}$(ii) ${\mathrm{CuCO}}_3\cdot \mathrm{Cu}(\mathrm{OH}{)}_2\stackrel{\mathrm{HCl}}{⟶}{\mathrm{CuCl}}_2+{\mathrm{CO}}_2\uparrow +{\mathrm{H}}_2\mathrm{O}$${\mathrm{CuCl}}_2\stackrel{\mathrm{K}()}{⟶}\underset{\mathrm{ppt}}{{\mathrm{C}}_2{\mathrm{l}}_2}\downarrow +\mathrm{KCl}+{\mathrm{I}}_2$(b) For Copper Glance ${\mathrm{cu}}_2\mathrm{S}-\frac{\text{ Roasting }}{{\mathrm{O}}_2}{\mathrm{cu}}_2\mathrm{O}+{\mathrm{SO}}_2\uparrow$${\mathrm{Cu}}_2\mathrm{S}+{\mathrm{Cu}}_2\mathrm{O}⟶\mathrm{Cu}+{\mathrm{SO}}_2\uparrow$${\mathrm{SO}}_2$ is the gas which gives green colour with acidified ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$$3{\mathrm{SO}}_2+{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+{\mathrm{H}}_2{\mathrm{SO}}_4⟶{\mathrm{K}}_2{\mathrm{SO}}_4+{\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3+4{\mathrm{H}}_2\mathrm{O}$