Combustion of an organic compound:

During analysis of a sample of an organic compound, we use the apparatus shown above. Trap 1 is
connected directly to Trap 2. It is safer to suck air out of Trap 4 as opposed to blowing it into Trap 1 to
avoid blowing out the stoppers of the traps and to avoid liquid in Traps 2 and 3 from being blown into
Trap 4.
1) The purpose of Trap 1 is to make sure that the air that passes over the heated sample is free of
carbon dioxide and water vapor.
2) Role of solid KOH: Solid KOH absorbs carbon dioxide and water vapor
3) Purpose of Trap 2: The purpose of trap 2 is to absorb all the water produced as a result of burning
the sample of the compound.
4) Role of concentrated sulfuric acid: Concentrated H2SO4 absorbs water only.
5) Role of solid calcium chloride: Solid CaCl2 absorbs water only
6) The purpose of Trap 3 is to absorb carbon dioxide produced as a result of burning the sample of
the compound.
7) The purpose of Trap 4 is to prevent any carbon dioxide from going backward.
8) Trap 3 containing KOH solution should come after Trap 2 containing concentrated H2SO4
because KOH solution gives off water vapor so we will not be able to tell how much water comes
from burning the compound.


Hygroscopic liquid: is a liquid that absorbs water from the surrounding air. For example,
Concentrated sulfuric acid, H2SO4(l).

Deliquescent solid: is a solid that absorbs water from surrounding air. For example: potassium

hydroxide, KOH(s), calcium chloride, CaCl2 (s) and sodium chloride, NaCl (s)