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Difficulty: MediumSublimation, Magnetization, and Centrifugation

A sample of crude naphthalene contaminated with non-volatile inorganic salts is subjected to gentle heating under a cool watch glass. The naphthalene deposits on the underside of the watch glass as pure crystals without melting first. Which fundamental property of naphthalene enables this method of purification?

  1. A relatively high vapor pressure as a solid, enabling direct transition from solid to vapor phase upon heatingAnswer
  2. B
    A large difference in boiling points between the components when dissolved in a liquid medium
  3. C
    Thermal instability causing chemical decomposition into gaseous elements followed by recombination
  4. D
    A dramatic increase in aqueous solubility at elevated temperatures compared to room temperature

Answer

A relatively high vapor pressure as a solid, enabling direct transition from solid to vapor phase upon heating
Sublimation relies on the physical property of certain solids (like naphthalene, iodine, camphor, and ammonium chloride) to exert a high vapor pressure below their melting point, transitioning directly from solid to vapor phase upon heating.

Step-by-Step Solution

1
Identify the separation technique described in the scenario
The process described (solid converting directly to gas and re-depositing on a cool surface without passing through a liquid state) is sublimation.
Sublimation occurs when a substance undergoes a direct phase transition from solid to gas upon heating.
2
Determine the physical property responsible for sublimation
Sublimable solids possess weak intermolecular van der Waals forces and a high vapor pressure in the solid state.
When heat energy is applied, molecules overcome lattice forces and escape directly into the vapor phase without forming a liquid.

Key Concept

Sublimation physical principle
Estimated Time:1m 0s
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Topics

Sublimation, Magnetization, and Centrifugation