Answer the following questions briefly:
(i). What is the actual reducing agent of haematite in blast furnace?
(ii). Zinc, not copper is used for the recovery of metallic silver from the complex `[Ag(CN)_2]^(ɵ)`, explain.
(iii). Why is chalcocite roasted and not calcinated during the recovery of copper?

Explanation

(i). For iron, first by calcination and roasting the ferrous oxide is oxidised to ferric. Then in blast furnace,
Smelting is done where it is reduced to iron.
`4FeO+O_2to2Fe_2O_3`
`Fe_2O_3+COto2Fe_3O_4+CO_2`
`Fe_2O_3+COto2FeO+CO_2`
`FeO+COtoFe+CO_2`
Carbon monoxide is the actual reducing agent of haematite in blast furnace.
(ii). Zinc is more reducing and cheaper than copper.
(iii). Chalcocite is a sulphide ore of copper therefore it must be roasted in the presence of air to get oxide.