A mixture of sand and naphthalene can be separated by which method?

The separation of a mixture of sand and naphthalene is a classic example of using the sublimation method in chemistry. Sublimation is a process in which a substance changes directly from a solid state to a gaseous state without passing through the liquid phase. Upon cooling, the vapors condense back into solid form. This property is observed in certain compounds like naphthalene, camphor, iodine, and ammonium chloride.

In the given mixture, sand is a non-volatile and non-sublimable substance, meaning it does not vaporize or decompose at the temperatures where naphthalene sublimes. When the mixture is gently heated, the naphthalene crystals sublimate, forming vapors that can be collected on a cold surface, such as a watch glass or the lid of a Petri dish. The sand remains behind as residue. When these vapors cool, they re-solidify into pure naphthalene crystals, effectively separating the two components.

This method is particularly useful for separating volatile solids from non-volatile impurities or other substances that do not sublime under similar conditions. It does not involve any liquid phase, making it suitable for materials that might react with solvents or decompose when melted.

Key Steps in the Sublimation Process:

1. 
   

   Place the mixture in a china dish or sublimation apparatus.

   
   


2. 
   

   Cover it with an inverted funnel or lid to collect vapors.

   
   


3. 
   

   Gently heat the mixture.

   
   


4. 
   

   Allow the vapors to condense on the cool surface.

   
   


5. 
   

   Scrape off the purified naphthalene crystals.

   
   

Applications:

• 
  

  Purification of volatile solids such as naphthalene, iodine, camphor, and benzoic acid.

  
  


• 
  

  Used in chemical laboratories to separate organic compounds from inorganic impurities.

  
  

Thus, sublimation is the correct method to separate a mixture of sand and naphthalene, as only naphthalene sublimes upon heating while sand remains unchanged.