Chemistry · General Principles Of Organic Chemistry · NEET
Only solids that sublime, meaning they go straight from solid to vapour on heating without melting. Common NEET examples are camphor, naphthalene, benzoic acid, anthracene and iodine. If a solid melts first (like most sugars or salts), sublimation cannot be used.
Sublimation works only when the wanted compound turns to vapour but the impurity does not. The impurity stays behind as a solid while the pure vapour rises and re-deposits on a cold surface. If the impurity also sublimed, both would rise together and no separation would happen.
Evaporation is liquid changing to vapour. Sublimation is solid changing to vapour with no liquid stage in between. In purification, evaporation removes a solvent, while sublimation directly lifts a pure solid compound away from its solid impurities.
The impure solid is heated in a dish. A cold surface (an inverted funnel or a cold watch glass) is placed above it. The compound sublimes, rises as vapour, hits the cold surface, cools and re-solidifies there as pure crystals. The non-volatile impurity is left in the dish.
No. In true sublimation the vapour turns straight back into solid on the cold surface. This reverse process (vapour to solid) is called deposition. No liquid appears at any stage, which is the whole point of the method.
On heating, some solid substances change from the solid to the vapour state without passing through the liquid state. The technique used for the purification of such substances based on the above principle is known as:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Camphor, naphthalene, benzoic acid, anthracene and iodine are the standard examples. These solids sublime cleanly, so NEET often uses them in sublimation questions.
Only for solids. Liquids are purified by distillation. Remembering this one line helps you reject distraction options quickly in the exam.
The compound must sublime (solid to vapour, no melting) and the impurity present must be non-volatile so it stays behind.
It is a physical change. Only the physical state changes from solid to vapour and back to solid; the chemical identity of the compound stays the same.
It is one of the basic purification methods in the Organic Chemistry chapter and is asked directly, as in NEET 2024. Knowing its principle and examples earns easy, high-certainty marks.
