physical chemistry – Why does a mixture of siloxene and cerium(IV) sulfate luminesce?

The Question :

25 people think this question is useful

I performed an experiment where siloxene and cerium(IV) sulphate were mixed together: when I did so the mixture produced an orange-yellow glow. Why does it glow? What is it about the two chemicals in particular that makes this happen?

Method for synthesising siloxene:

Carefully measure out 50 cm3 of concentrated hydrochloric acid into a 100 cm3 measuring cylinder. Put the acid in a 1 dm3 beaker containing a magnetic stirrer bar and place the beaker on a heater/magnetic stirrer.

Switch on the stirrer and slowly add 5 g of calcium silicide, one spatula measure at a time, to the stirred acid. Continue stirring the mixture until the reaction subsides.

Measure out a further 25 cm3 of concentrated hydrochloric acid and carefully add this to the stirred mixture. Now turn the heater on and heat the mixture to boiling. Boil the mixture for five minutes. After boiling, slowly add 150 cm3 of distilled water then boil again for approximately five minutes.

Switch off the heater and leave the mixture stirring while it cools.

Set up a Buchner funnel and flask in a fume cupboard.

Carefully pour the yellow siloxene that you have made onto a filter paper in a Buchner funnel (try to leave the unreacted grey/black solid calcium silicide in the beaker). Now wash your sample of siloxene – first with 10 cm3 of ethanol and then with 10 cm3 of ethoxyethane. Drawing air through the sample will help to dry the yellow, solid siloxene.

Method for producing the glow:

Place 0.8 g of siloxene and 75 cm3 of 1M sulfuric acid in a 250 cm3 conical flask. In a second 250 cm3 conical flask, dissolve the 0.5 g of cerium(IV) sulphate in 75 cm3 of 1M sulphuric acid. Label and stopper both flasks.

Go into a dark room. Turn out the light, add the cerium(IV) sulphate to the siloxene and swirl the mixture. You should see a fairly bright orange-yellow glow.

The Question Comments :
  • Maybe someone can access the following paper: Grigorenko, F. F., and L. I. Dubovenko. “Chemiluminescence in the reaction of siloxene with cerium (IV) sulphate.” UKr. khim. Zh 1968, 34, 1294-1299.
  • I am not sure, did you mean siloxane

The Answer 1

3 people think this answer is useful

The idea of chemiluminescence is pretty simple, you need an oxidizer and a substance that actually gives a glow.

According to Wikipedia cerium sulfate is rather an oxidizer especially under acidic condition, which actually explains why we need sulfuric acid, so basically, whatever is siloxene (I suspect it is a silicon oxide kind of structure) it is an oxidant that when oxidizes the difference in energy level causes a glow in the visible spectrum.

Unless more clarification about siloxene, this could be the only possible answer.


  • NurRage explanation about chemiluminescence
  • Wikipedia for properties about cerium sulfate

EDIT: what was meant by potential sources is that the method of using words was mine but the information is from the sources sorry for inconvenience

The Answer 2

3 people think this answer is useful

According to this paper:

“Siloxene is a yellow silicate polymer obtained from the reaction of
calcium silicide with hydrochloric acid.”

Also, from the same paper:

“The basic structure [of siloxene] is randomly substituted by hydroxyl
and chlorine groups and this affects both the CL [chemoluminescence]
spectrum and the CL efficiency. CL emission in the red region of the
spectrum results from the reaction of siloxene with oxidants such as
ceric sulfate, chromic acid, potassium permanganate and nitric acid.”

This brief explanation would appear to me to equally apply to the luminescence observed in the question.

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