2.7 Distillation and Sublimination

Evaporation and Condensation:

• Evaporation (or vaporization) is the process of heating a liquid to turn it into a gas.

• Example: Water from hot tea turning into vapors.

• Condensation is the process of cooling vapor to turn it back into a liquid.

• Example: Water vapor cooling and turning into liquid water.

Distillation:

• Distillation is the process of heating a liquid to turn it into vapor, and then cooling the vapor to retrieve the liquid.

• Formula: Distillation = Vaporization + Condensation.

• It is often used to separate volatile substances from a mixture.

Sublimation:

• Sublimation is the process in which a solid directly turns into a gas without passing through the liquid phase.

• Example substances: Ammonium Chloride (NH₄Cl), camphor (C₁₀H₁₆O), naphthalene (C₁₀H₈), solid carbon dioxide (CO₂), Iodine (I₂), Aluminum chloride (AlCl₃).

Experiment 7: Sublimation of Aluminum Chloride (AlCl₃)

• Take solid aluminum chloride (AlCl₃) in a beaker, and place a glass lid over it. Add ice cubes on top of the lid.

• Apply heat slowly. You will observe the solid AlCl₃ turning directly into a gas. This gas will then cool under the lid and condense back into a solid.

Key Points:

• Sublimation occurs when a solid directly turns into gas without becoming a liquid.

• Substances that undergo sublimation can be separated from other solid substances using the sublimation process.

• Example: Ammonium chloride (NH₄Cl) can be separated from salt (NaCl) by sublimation.

• Iodine in iodized salt sublimes when heated and can be retrieved by cooling the vapor into solid iodine.

Important Notes:

• Sublimated substances like iodine, ammonium chloride, and camphor do not become liquid when heated but directly vaporize.

• Sublimation can be used for separating substances in mixtures, as in the case of iodized salt and sand and glucose (which do not have sublimated substances).