sublimation

Question 1

definition

Answer 1

The process of converting solid substances in to vapours by heating and then condensing it back to the
solid state, without passing it through the intermediate liquid state, is called sublimation.

Question 2

explanation

Answer 2

 The condensed solid is called sublime.
 Usually the solid first coverts in to liquid state before being converted in to vapour state but in
sublimation liquid phase do not exist.
 Thus,

Question 3

triple point

Answer 3

 The point having a different pressure and temperature at which the solid, liquid, and vapour phases of
a chemical entity are able to co-exist indefinitely is called triple point.

Question 4

principle

Answer 4

A solid sublime only when the pressure of its vapour is below that of the triple point for that substance.
This principle can be explained by following graph.
 The line OA indicates the melting point of the substance and along this line solid and liquid is at
equilibrium. On right side of this line only liquid exists while on left side only solid exists.
 The line OB indicates the vapour pressure of the solids vapours and this curve is called vapour pressure
curve. Above this line only liquid exists and below this only vapour present.
 The line CO is called sublimation curve and represents the conditions of temperature and pressure for
the co-existence of solid and vapour phase.
 To right side of this line only vapour exists and on left side of line only solid exists.
 The point O the intersection of three lines is called triple point. And the graph shows if the vapour
pressures of vapour, formed by the solid, less than the triple point, it will directly pass from solid to
vapour and vapour to solid.

Question 5

procedure

Answer 5

 The impure substance is placed in the china dish which is then gently heated on the stand bath. The
dish is covered with the perforated filter paper over which is placed an inverted funnel.
 The surface of which may be kept wet by covering it with wet filter paper or cotton plug. The vapour
rising from, the solid pass through the holes in the filter paper and are deposited as pure solid on the
wall of the funnel. The filter paper performs two functions
 It does not permit the sublime substance to drop back in to the dish.
 It keeps the funnel cool by cutting off the direct heat from the dish.

Question 6

application

Answer 6

 Sublimation is very helpful in separating volatile substances from nonvolatile solids. In this way pure
substance are obtained which are used in various processes.
 Some valuable chemical substances such as naphthalene, camphor, and benzoic acid etc are purified
by this process.