A mixture contains solid naphthalene (melting point 80°C) and solid sodium chloride. Naphthalene sublimes readily when heated, while sodium chloride does not. Which method is most appropriate to separate and obtain pure naphthalene?
Show the answer and explanation
Correct answer
B. Heat the mixture gently and collect the sublimate on a cold surface
Principle or equation
Sublimation is the direct transition from solid to gas. Substances that sublime can be separated from non-volatile solids by heating and condensing the vapor on a cold surface.
Why this answer is correct
Naphthalene sublimes on heating, leaving sodium chloride behind. The vapor can be collected and cooled to re-form solid naphthalene. The other methods are not suitable because naphthalene is not very soluble in water and does not react with acid.
Example
Heating a mixture of iodine and sand: iodine sublimes and deposits on a cold watch glass, leaving sand.
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