JEE Main 2021 · 27 July · evening · Single correct · +4 / −1
The addition of silica during the extraction of copper from its sulphide ore :-
- (a) converts copper sulphide into copper silicate
- (b) converts iron oxide into iron silicate
- (c) reduces copper sulphide into metallic copper
- (d) reduces the melting point of the reaction mixture
Answer and solution
Answer (b) converts iron oxide into iron silicate
Solution
Chemistry ma’am · 4 steps
Silica is a flux here: it grabs the iron oxide impurity and carries it away as slag.
- The impurity. Copper pyrites, CuFeS₂, carries a lot of iron. During roasting, iron sulphide is oxidised to iron oxide: 2FeS + 3O₂ → 2FeO + 2SO₂.
- Silica as flux. FeO is a basic oxide and silica is an acidic flux. In the blast furnace they combine to form ferrous silicate, the slag.
FeO + SiO₂ → FeSiO₃ (slag)
- Slag floats off. The light, molten slag floats on top and is removed. What is left below is copper matte, mostly Cu₂S with a little FeS.
- So. Silica turns iron oxide into iron silicate, which is option (b). Copper stays as Cu₂S and is reduced later by self-reduction, not by silica.
The idea to keep. Match the flux to the impurity: an acidic flux like SiO₂ removes a basic impurity like FeO, and a basic flux like CaO removes an acidic one like SiO₂.
Answer from the NTA final answer key. Solution by PrepWiser.