Sublimation

Sublimation is a special process where a solid changes directly into a gas without becoming a liquid first.

• Normally, when a solid is heated, it first melts into a liquid and then the liquid evaporates into a gas. But in sublimation, a solid skips the liquid phase and goes directly into the gaseous state.
• Example: When iodine crystals are heated, they don’t melt into liquid. Instead, they change directly into iodine gas (fumes).

Sublimation Method:

Sublimation in chemistry refers to the phase transition in which matter changes state from a solid immediately into a gas, without passing through an intermediate liquid phase. Sublimation occurs when atmospheric pressure is too low for a substance to exist in liquid form. Sublimation is the inverse of deposition, the phase transition in which gas goes immediately to a solid state. Whether or not a substance will sublimate from a solid to a gaseous state depends on the triple point of the substance, the temperature and pressure at which a substance exists in equilibrium as the three states of matter.

A substance will only sublimate at temperatures and pressures lower than the substance’s triple point.

Application:

• Used in air freshener solids

1. Aim: To observe the sublimation of iodine crystals when heated with sand.

2. Requirements: sand, iodine crystals, crucible, tripod, funnel, cotton plug, and burner.

3. Procedure

• Setup: Take some sand in a crucible and place a few iodine crystals on top.
• Heating Assembly: Position the crucible on a tripod.
• Funnel preparation: Block the stem of a funnel with a cotton plug and invert it over the crucible.
• Heating: Light the burner and heat the mixture in the crucible.
• Observation: Carefully observe the changes, noting the sublimation of iodine.

4. Conclusion: The iodine crystals transition from a solid to a gaseous state without passing through a liquid phase, demonstrating the process of sublimation.

Sublimation

Experiment of the separation of ammonium chloride and salt by sublimation.

Aim: To check sublimation.

Requirements: Salt, ammonium chloride, inverted funnel, china dish, cotton plug, burner.

Procedure:

• Take some mixture of salt and ammonium chloride.
• Put an inverted funnel over the china dish.
• Put a cotton plug on the stem of the funnel.
• Now, heat slowly and observe.

Observation: Ammonium chloride on heating, was evaporated and salt was left behind.

Result/ Inference: Ammonium chloride changed its state directly from solid to gas without changing into a liquid state. Hence, salt got separated.