Question

In an experiment set up for sublimation a perforated absostos sheet is placed between the China dish and funnel . what is its purpose

Answer 1

Sublimation is the process by which volatile solid substances passes directly  from the solid state to the gaseous state when heated.

The sublimation process in organic chemistry is usually used to separate volatile solids like camphor and Naphthalene and from non - volatile ones.  
In a sublimation experiment different apparatus can be used to illustrate this process as follows

- China dish 
- Funnel
- Asbestos paper

Steps followed:

i)The mixture of the volatile and non-volatile solids are placed in a china dish.
ii) The mixture is the covered by a perforated asbestos sheet. 
iii)The mixture in the china dish is covered by a funnel, inverted over it. 
iv)This mixture is then heated gently - making the volatile solid sublime passing through the perforated asbestos sheet.

The volatile solid the condenses on the inner wall of the funnel, separating it from the non volatile one.

The function of the perforated asbestos sheet is to act as a sieve separate the mixture and prevent the re-mixing of the two solids after separation.