Deck 10: Sublimation

Question 1

Which of the following compounds could be subjected to sublimation at atmospheric pres- sure?
a) Compound A: vapor pressure at its melting point = 770 mm Hg
(b) Compound B: vapor pressure at its melting point = 400 mm Hg
(c) Compound C: vapor pressure at its melting point = 10 mm Hg

Answer 1

Compounds A and B will have significant vapor pressure at their melting point.

Question 2

In the preceding problem, which compounds could be vacuum sublimated?

Answer 2

Only compund C. The others would have such significant vapor pressure in a vacuum that they would be lost into the vacuum system.

Question 3

3 Which of the following compounds would be likely to evaporate readily? Explain your answer.

Answer 3

Only (b) and (c). Fenchone will evaporate readily because it is spherically shaped. Pentacene will evaporate becaue it is cylindricaly shaped. Hexadecane has a zig-zag shape and strong van der Waal attractions.

Question 4

You have a mixture of p-nitrobenzaldehyde (vapor pressure 0.01 at its melting point of 106˚) and camphor. Explain how you would separate these two compounds by sublimation. How would you perform the sublimation if benzoic acid instead of camphor is used?