Chemistry Reference
In-Depth Information
Appendix B. Experiments
E5.1: Gas Chromatography in a School Experiment
Problem: Usual chromatographs for research laboratories are closed instruments,
into which you cannot look (“black boxes”). For understanding the analytical
process, it is therefore educationally reasonable to demonstrate an apparatus,
which uses a vitreous coiled-tube condenser made of glass which shows all
functions openly (see figure). With this apparatus propane and both isomers of
butane can be separated and detected by a luminous flames.
Material: Gas chromatograph, gas syringe (10mL), butane burner (F
+
); hydrogen (F
+
).
Butane
Hydrogen
Carrier substance
With hexadecane
Procedure: The coiled-tube condenser contains a white carrier substance. The
surface of the carrier substance is coated with nonevaporating hexadecane
(C
16
H
34
) and therefore it can be used for the separation of hydrocarbons. Hydrogen
is being connected and passed through as carrier gas. In case the hydrogen-oxygen
reaction is negative, hydrogen can be ignited at the end of the glass tube.
The gas syringe is being filled with gas from the butane burner, and 5 mL has to be
injected into the hydrogen stream through the septum. One waits until the colorless
hydrogen flame changes for a short time into a yellow flame. The experiment is
being finished by turning off the hydrogen stream.
Observation: After about 30 s the colorless hydrogen flame lights up bright yellow
and then goes colorless again. That repeats two other times: the first yellow flame
shows propane, the second one
i
-butane, the third one
n
-butane.
