Question

Describe an experiment to demonstrate the process of sublimation.

Answer 1

Sublimation is the process of converting materials from a solid to a gaseous state without passing through a liquid state. Sublimation is the term used by those of us who are interested in the water cycle to describe the process of snow and ice turning into water vapour in the air without first melting into water.

Complete answer:
Sublimation is the process of a material transitioning directly from a solid to a gas state without going through a liquid stage. Sublimation is an endothermic process that happens when a material's triple point on its phase diagram, which corresponds to the lowest pressure at which the material can exist as a liquid, is reached. Deposition is the reversal of sublimation, in which a material transitions from a gas to a solid state.

Experiment: Fill a china dish halfway with ammonium chloride powder. To prevent vapours from escaping, cover the china dish with an inverted funnel and a cotton stopper at the funnel's end. Assemble the equipment as directed. A burner is used to heat the dish.Ammonium chloride evaporates when it is solid. When it comes into touch with the funnel's walls, it cools, solidifies, and is deposited there.

Chemists utilise the process of sublimation to purify substances. A solid is generally heated under vacuum in a sublimation device. The solid volatilizes and condenses as a refined chemical on a cooled surface (cold finger) under this decreased pressure, leaving a non-volatile residue of impurities behind. The purified chemical can be recovered from the cooling surface once the heating has stopped and the vacuum has been eliminated.

A temperature gradient is used for even better purification efficiency, as well as the separation of various fractions. In most cases, an evacuated glass tube is used, which is progressively heated in a regulated manner. The material flows from the hot end, which contains the starting material, to the cool end, which is attached to a pump stand.

The operator can control the zones of re-condensation by controlling temperatures along the length of the tube, with very volatile compounds pumped out of the system completely (or caught in a separate cold trap), moderately volatile compounds re-condensing along the tube according to their different volatilities, and non-volatile compounds remaining in the hot end.

Note: At temperatures below the freezing/melting point temperature line at $0{\text{ }}^\circ C$ for partial pressures below the triple point pressure of 612 Pa, snow and ice sublime, though more slowly (0.0006 atm). The substance to be dehydrated is frozen, and its water is allowed to sublime under decreased pressure or vacuum during freeze-drying. Sunshine hitting directly on the topmost layers of the snow causes the loss of snow from a snowfield during a cold period. Sublimation and erosive wear of glacier ice are part of the ablation process.