Sublimation

Sublimation occurs in substances that possess weak intermolecular forces — typically weak van der Waals forces or dipole–dipole interactions.

When heat is supplied, surface particles of the solid gain sufficient kinetic energy to completely overcome these weak intermolecular attractions and escape directly into the gaseous phase — without first accumulating into a liquid.

The change of a solid substance directly into a gas or vapour without first changing into a liquid is called sublimation.

OR

The change from solid state to vapour state without passing through the liquid state is called sublimation, and the substance is said to sublime.

Aim

To demonstrate sublimation and separate iodine from sand using the process of sublimation.

Materials Required

China dish, tripod stand, wire gauze, Bunsen burner, glass funnel, cotton plug, iodine crystals, sand.

Procedure

1. Place a small quantity of sand in a clean, dry china dish.
2. Add a few iodine crystals on top of the sand.
3. Place the china dish on a tripod stand with wire gauze.
4. Plug the narrow stem of a glass funnel tightly with a cotton plug to prevent vapours from escaping.
5. Invert the plugged funnel over the china dish.
6. Heat gently using a Bunsen burner at low flame.
7. Observe the changes inside the funnel and in the china dish continuously.
8. Allow the apparatus to cool completely before removing the funnel.

Observations and Inferences

Result and Conclusion

On heating, iodine changes directly from solid to gas (sublimation) and on cooling forms solid crystals again, while sand remains behind, showing that sublimation can separate a sublimable solid from a non-sublimable one.