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General Principles of Isolation of Elements · Question 22

AIPMT 2007MCQMedium📈 Topic in 25% papers+4−1
1

Which of the following statements about the advantage of roasting of sulphide ore before reduction is not true?

  1. The fG of the sulphide is greater than those for CS2 and H2S.
  2. The fG is negative for roasting of sulphide ore to oxide.
  3. Roasting of the sulphide to the oxide is thermodynamically feasible.
  4. Carbon and hydrogen are suitable reducing agents for metal sulphides.

Answer

(4) Carbon and hydrogen are suitable reducing agents for metal sulphides.

Solution

∵ fG of a metal sulphide is more negative than that of CS2 and H2S (CS2 is in fact an endothermic compound),

⇒ rG for 2MS + C 2M + CS2 and MS + H2 M + H2S is positive.

⇒ Carbon and hydrogen cannot reduce metal sulphides, so statement (4) is not true.

As per NCERT, sulphide ores are therefore first roasted to oxides, e.g. 2ZnS + 3O2 2ZnO + 2SO2; this change has negative G , i.e., it is thermodynamically feasible (statements (2) and (3) true).

⇒ The oxide is then easily reduced by carbon, e.g. ZnO + C coke, 1673 K Zn + CO.

∴ The statement that is not true is (4).

Answer: (4)

Out of syllabusAIPMT 2007

Keep practising — General Principles of Isolation of Elements

2

The mass of carbon anode consumed (giving only carbon dioxide) in the production of 270 kg of aluminium metal from bauxite by the Hall process is (Atomic mass : Al = 27)

  1. 270 kg
  2. 540 kg
  3. 90 kg
  4. 180 kg
AIPMT 2005
3

The method of zone refining of metals is based on the principle of

  1. greater mobility of the pure metal than that of the impurity
  2. higher melting point of the impurity than that of the pure metal
  3. greater noble character of the solid metal than that of the impurity
  4. greater solubility of the impurity in the molten state than in the solid
Out of syllabusAIPMT 2003

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