Ammonium chloride can be separated from its mixture with common salt by

Analysis

The question asks for the most effective method to separate a mixture of two solids: Ammonium chloride ($NH_4Cl$) and common salt (Sodium chloride, $NaCl$).

Concept

To choose the right separation technique, we must look at the physical properties of the substances involved:

1. Sodium chloride ($NaCl$): This is a stable ionic salt that remains solid at high temperatures and does not change state until it reaches its very high melting point.
2. Ammonium chloride ($NH_4Cl$): This is a covalent compound that exhibits the property of sublimation. Sublimation is the process where a solid changes directly into a gas without passing through the liquid state when heated.

Solution

• Step 1: Place the mixture in an evaporating dish or a beaker.
• Step 2: Apply heat to the mixture.
• Step 3: As the temperature rises, the ammonium chloride will sublime (turn into vapor).
• Step 4: You can collect the ammonium chloride vapor by placing an inverted funnel or a cold surface over the container, where it will deposit back into a solid state (desublimation).
• Step 5: The common salt ($NaCl$) will remain behind in the container because it does not sublime.

Other options like distillation, evaporation, and decantation are not suitable here because they are designed for separating liquids from solids or liquids from liquids, not for separating two solids based on thermal behavior.

Conclusion

Since ammonium chloride sublimes upon heating while common salt does not, sublimation is the correct physical method for this separation.

Exam Tip

Whenever you see a question involving Ammonium chloride ($NH_4Cl$), Iodine ($I_2$), or Naphthalene (mothballs) in a mixture, immediately think of sublimation. These are the most common substances tested in JAMB that undergo this process!