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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper I covers inorganic chemistry.

UPSC Combined Geo-Scientist, Mains · 2017 · Mains Paper I

Q11(a). pH control in sulfide separations

Question

In qualitative inorganic analysis, H₂S is passed in acidic medium for Group II metal ions while for Group III B metal ions the same is passed in basic medium. Provide an explanation.

Answer in brief

Acid suppresses sulfide-ion concentration so only the least soluble sulfides precipitate; alkaline conditions increase sulfide concentration enough to precipitate the less insoluble sulfides.

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CoverspH control in sulfide separationsQualitative analysis

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