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How many of the following statements about solutions and azeotropes are correct? (i) Azeotropes obey Raoult's law. (ii) A minimum-boiling-point azeotrope is formed when the heat of mixing is negative (DeltaH_mix < 0). (iii) The molar heat of vaporization (DeltaH_vap) of an ideal dilute aqueous solution containing a non-volatile solute equals that of pure water. (iv) When an azeotrope is vaporized, the composition of the vapor formed is identical to that of the liquid.

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

Statement (i) is false: azeotropes deviate from Raoult's law. Statement (ii) is false: minimum-boiling azeotropes arise from positive deviations (DeltaH_mix > 0, weaker A-B interactions). Statement (iii) is true for ideal solutions since DeltaH_mix = 0 leaves intermolecular attractions unchanged. Statement (iv) is true by the very definition of an azeotrope. So 2 statements are correct.

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