Sublimation

The main aim of this experiment is to purify solid ammonium chloride from impure via a sublimation process.

Sublimation refers to a phenomenon of transformation or conversion of a substance from the solid phase into a gas phase without passing or changing through an intermediate liquid phase. The term sublimation only applies to the physical change of state of a substance and not to the transformation of a solid into a gas during a chemical reaction.

To perform this experiment, apparatus and materials are required: ammonium chloride (s), watch glass, bunsen burner, tripod Stand, wire gauge, china dish, funnel, cotton plug, and spatula.

To purify ammonium chloride via the sublimation process, we have to follow the given procedure.

Take powdered sublimable solid (ammonium chloride) in a china dish.
Place the tripod stand along with the wire gauze over the burner.
Place the china dish containing ammonium chloride over the wire gauze on the tripod stand.
Put an inverted funnel over the china dish.
Insert a cotton plug into the stem of the funnel.
Heat the china dish slowly with the help of the Bunsen burner.
After the entire solid mass has sublimed, stop heating and let the funnel cool down. Remove the funnel and record your observation.

In this experiment, we have learnt that:

The process of conversion of a solid to its gaseous state directly on heating is called sublimation. Ammonium chloride is a sublimable solid as it gets converted to its vapour on heating. However, the vapours of ammonium chloride convert to their solid state on cooling. This process is called deposition.

FAQs on Sublimation

Q.1: What happens to the atoms during sublimation?

Ans: The sublimation process is an endothermic process where atoms in a solid state absorb energy and gets converted to a gaseous state.

Q.2: What is the process for conversion of the gaseous phase to the solid phase?

Ans: The process for conversion of the gaseous phase to the solid phase is known as deposition or desublimation by keeping the pressure and temperature below the triple point.

Q.3: How would you separate a sand and naphthalene mixture?

Ans: By sublimation, sand and naphthalene mixture can be separated as naphthalene is a volatile substance that sublimes to vapours, and sand remains.

Q.4: What are examples of sublimating substances?

Ans: Benzoic acid, ammonium chloride, camphor, naphthalene, and iodine are volatile, so these are examples of sublimating substances.

Q.5: Is heat required for sublimation?

Ans: Yes, heat is required for sublimation. The amount of heat energy that must be delivered to a solid mole under constant pressure to turn it directly into a gas without going through the liquid phase is known as the sublimation enthalpy.