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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3so031

Liquids A (boiling point ) and B (boiling point ) form a mixture that has a constant-boiling azeotrope at under . Which statements are correct?

  1. AThe system shows negative deviation from Raoult's law
  2. B is negative
  3. CAt the azeotropic composition the total vapour pressure at a fixed temperature is a minimum compared with neighbouring compositions
  4. DSimple distillation of any composition finally gives pure A as the distillate

Answer: A, B, C

An azeotrope boiling above both pure components has a vapour pressure below the ideal value, which means negative deviation, stronger A-B interactions and an exothermic mixing. At fixed temperature, lower vapour pressure at the azeotropic composition means a minimum in the P-x curve. Distillation moves toward the azeotrope, so pure A is not obtained from every starting composition. Answer: 1, 2 and 3.
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