Question

The compound that can be purified by sublimation is :

• A. Ammonium Chloride
• B. Calcium Carbonate
• C. Sodium Carbonate
• D. Aluminium Chloride

Hint:

Sublimation is solid \(\rightarrow\) gas directly. Think of substances that "disappear" as solids when heated and reappear as solids when cooled, without melting. Common examples are ammonium chloride, camphor, naphthalene, and iodine. Ammonium chloride is a key example to remember for this process.

Answer 1

The Correct Option is A

Concept: Sublimation is a process where a substance transitions directly from the solid phase to the gas phase without passing through the liquid phase. This property can be used for purification if one component of a mixture sublimes while others do not. Step 1: Understanding Sublimation for Purification If a mixture contains a sublimable substance (one that can sublime) and non-sublimable impurities, heating the mixture will cause the sublimable substance to turn into vapor. This vapor can then be cooled and condensed back into a solid in a separate location, leaving the impurities behind. Step 2: Identifying substances that sublime Common substances that readily sublime at or near atmospheric pressure include:
Iodine
Naphthalene (mothballs)
Camphor
Dry ice (solid Carbon Dioxide)
Ammonium Chloride (\(NH_4Cl\)) Step 3: Analyzing the options
(1) Ammonium Chloride (\(NH_4Cl\)): This is a well-known example of a compound that sublimes upon heating. It transitions directly from solid to gas and can be condensed back to solid.
(2) Calcium Carbonate (\(CaCO_3\)): Also known as limestone or chalk. It does not sublime under normal heating conditions; instead, it decomposes at high temperatures (e.g., \(>800^\circ C\)) into calcium oxide and carbon dioxide.
(3) Sodium Carbonate (\(Na_2CO_3\)): Also known as washing soda. It is a stable ionic solid that melts at a high temperature (\(851^\circ C\)) but does not typically sublime.
(4) Aluminium Chloride (\(AlCl_3\)): Anhydrous aluminium chloride is a covalent compound that sublimes at around \(180^\circ C\). This is also a substance that can be purified by sublimation. However, ammonium chloride is a more common textbook example for sublimation at a simpler level. Given that Ammonium Chloride is listed and is a classic example, it is the intended answer. If both were present and only one could be chosen, context or common knowledge emphasis would guide. Step 4: Conclusion Among the given options, Ammonium Chloride is a classic example of a compound that can be purified by sublimation. Aluminium Chloride also sublimes, but Ammonium Chloride is a very standard example in introductory chemistry.