JEE Main 2022 · 25 July · morning · Single correct · +4 / −1
The compound(s) that is (are) removed as slag during the extraction of copper is :
(A) CaO
(B) FeO
(C) Al₂O₃
(D) ZnO
(E) NiO
Choose the correct answer from the options given below:
- (a) (C), (D) only
- (b) (A), (B), (E) only
- (c) (A), (B) only
- (d) (B) only
Answer and solution
Answer (d) (B) only
Solution
Chemistry ma’am · 4 steps
Copper pyrites carries iron as the impurity, so silica turns FeO into slag and leaves the copper behind.
- Start from the ore. Copper is mostly extracted from copper pyrites, CuFeS₂. The big impurity is iron, so the whole process is built to get rid of iron.
- Iron becomes FeO. On roasting and smelting, iron grabs oxygen first and forms FeO. Copper has a stronger hold on sulphur, so it stays as Cu₂S, the copper matte.
FeO + SiO₂ → FeSiO₃
- Check the rest. CaO is the flux in the iron blast furnace. It is not the impurity removed here, because silica is the flux for copper. Al₂O₃, ZnO and NiO are not the impurities of copper pyrites, so they play no part in this slag.
- So. Only FeO leaves as slag, as iron silicate FeSiO₃. The answer is (d), (B) only.
The idea to keep. For slag questions, ask what the impurity is and what the flux is. In copper, FeO is the basic impurity and silica is the acidic flux. In iron, it is the other way round: CaO is the flux and silica is the impurity.
Answer from the NTA final answer key. Solution by PrepWiser.