JEE Main 2022 · 28 June · evening · Single correct · +4 / −1

In the metallurgical extraction of copper, following reaction is used :
FeO + SiO₂ → FeSiO₃
FeO and FeSiO₃ respectively are.

  1. (a) gangue and flux.
  2. (b) flux and slag.
  3. (c) slag and flux.
  4. (d) gangue and slag.
Answer and solution

Answer (d) gangue and slag.

Solution

Chemistry ma’am · 3 steps

Ask which one is the unwanted impurity, which one is added, and which one comes out as waste.

  1. Where FeO comes from. Copper pyrites, CuFeS₂, carries iron along with copper. On roasting, the iron sulphide turns into FeO, an unwanted impurity that has to be removed. That makes FeO the gangue here.
  2. Role of silica. FeO is basic, so an acidic flux, silica (SiO₂), is added to it. The flux combines with the impurity to form a fusible waste called slag.
    SpeciesRoleWhy
    FeOgangueiron impurity that must be removed from the copper ore
    SiO₂fluxadded on purpose to react with the impurity
    FeSiO₃slagfusible product that floats off and is thrown away
  3. So. In FeO + SiO₂ → FeSiO₃, FeO is the gangue and FeSiO₃ is the slag, which is option (d).

The idea to keep. Impurity + flux gives slag, every time. The impurity is the gangue, the substance you add is the flux, and the product you throw away is the slag.

Answer from the NTA final answer key. Solution by PrepWiser.

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Asked about 80 times in JEE Main since 2020. This question is from 2022.