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UPSC Combined Geo-Scientist

Chemist

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

Mains Paper II covers physical chemistry.

UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper II

Q15(a). Volume contraction on mixing

Question

Why does mixing 70.0 mL ethanol with 30.0 mL water at normal temperature and pressure give less than 100.0 mL total volume?

Answer in brief

Mixture volumes are not additive because molecular packing and interactions change; the ethanol–water mixture has a negative excess volume under these conditions.

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CoversVolume contraction on mixingPartial molar properties

All parts of Question 15