JEE Main · 2021 · 27 Jul 2021 · Shift 2 · General Principles and Processes of Isolation of Metals

The addition of silica during the extraction of copper from its sulphide ore

(A)reduces copper sulphide into metallic copper
(B)reduces the melting point of the reaction mixture
(C)converts copper sulphide into copper silicate
(D)converts iron oxide into iron silicate✓ Correct

Answer: (D)

Solution

Copper pyrites carries iron alongside copper, and roasting turns that iron into the basic oxide FeO, which would otherwise be reduced with the copper and contaminate it. Silica is added as an acidic flux and combines with this basic oxide during smelting:

FeO + Si O_{2} \to FeSi O_{3}

The silicate formed is light and fusible, so it floats as slag on the denser copper matte and is drawn off. The silica therefore converts iron oxide into iron silicate.

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JEE Main · 2021 · 27 Jul 2021 · Shift 2 · General Principles and Processes of Isolation of Metals

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