A mixture contains solid ammonium chloride and solid sodium chloride. Which method is most appropriate to separate and obtain pure ammonium chloride?
Show the answer and explanation
Correct answer
B. Heat the mixture gently; collect and cool the sublimed solid
Principle or equation
Ammonium chloride sublimes on heating, while sodium chloride does not; sublimation allows separation without decomposition.
Why this answer is correct
Heating the mixture causes NH4Cl to vaporize directly to gas, which can be collected on a cool surface and re-solidified. NaCl remains behind. Adding water would dissolve both, and filtration cannot separate dissolved solids. HCl would react with NH4Cl, and ethanol would not selectively dissolve one component.
Example
A mixture of NH4Cl and NaCl is heated in a sublimation apparatus; white NH4Cl crystals deposit on the cold finger, leaving NaCl in the dish.
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