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Chemistry Question 65 – NEET-UG 2024

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On heating, some solid substances change from solid to vapour state without passing through liquid state. The technique used for the purification of such solid substances based on the above principle is known as

Recall the different phase changes that matter can undergo, including solid to liquid, liquid to gas, and direct solid to gas.

Step 1: Understand the described phase change✦ Active

The question describes a process where a solid substance changes directly to a vapor state upon heating, bypassing the liquid state. This specific phase transition is known as sublimation.

Step 2: Relate the phase change to purification techniques○ Expand

Purification techniques often exploit differences in physical properties. For substances that sublime, this property can be used to separate them from non-subliming impurities.

Step 3: Identify the correct technique from the options○ Expand

Sublimation is the technique specifically designed to purify solids that undergo this direct solid-to-vapor transition. Distillation, chromatography, and crystallization involve different principles (boiling points, differential partitioning, and solubility, respectively) and typically involve a liquid phase at some point.

💡 Teacher's Secret Hint

Common examples of sublimable solids include camphor, naphthalene, iodine, and dry ice (solid carbon dioxide).

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