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General Principles of Isolation of Elements · Question 21

AIPMT 2007MCQEasy📈 Topic in 12% papers+4−1
1

Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

  1. Galena
  2. Copper pyrite
  3. Sphalerite
  4. Argentite

Answer

(4) Argentite

Solution

Galena (PbS), copper pyrites (CuFeS2) and sphalerite (ZnS) are concentrated by froth flotation.

As per NCERT, silver is leached from argentite (Ag2S) with a dilute solution of NaCN in the presence of air:

Ag2S + 4CN- 2[Ag(CN)2]- + S2-

⇒ 4S2- + 5O2 + 2H2O 2SO42- + 4OH- + 2S (air removes S2- and drives the leaching forward)

⇒ 2[Ag(CN)2]- + Zn [Zn(CN)4]2- + 2Ag

∴ Argentite is concentrated by chemical leaching.

Answer: (4)

Out of syllabusAIPMT 2007

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2

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.
Out of syllabusAIPMT 2007
3

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
4

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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