Introduction
"... heat cells are the part of ThermaCare® that provides warmth. These
cells contain a mixture of ingredients (activated carbon, iron powder, sodium
chloride, sodium thiosulfate, sodium polyacrylate and water) that react with
air to provide low-level heat. The chemical reaction is called iron oxidation,
which occurs naturally in the environment." (http://www.thermacare.com/Faq.aspx).
In the following experiment the chemical reaction between the air and the
ingredients of the heat cells will take place inside two 50 ml syringes connected
by a three-way cock.
In order to compare air with oxygen and with nitrogen the experiment will
be repeated by replacing the air by the other gases.
What to do
1. Measure the change of the volume of air during the reaction
of air and the ingredients of the cells of ThermaCare®.
2. Repeat the same reaction twice by replacing air by oxygen and the by nitrogen.
Material
Photo
1: Tray, scissors, 2 disposable syringes 50 ml, three-way cock, 1 ThermaCare®
(neck, wrist & shoulder), air, nitrogen, oxygen.
Experiment
1. Fill up one syringe with 50 ml of air, connect it
with the three-way cock (set it up to the 90° position).
2. Unpack one of the ThermaCare pieces, cut it into 10 heat cells, transfer
them into the second syringe.
3. Strongly press the plunger into the into this syringe cylinder.
4. Connect it with the cock (Photo
2).
5. In a synchronized fashion, push one of the syringe´s plungers and pull
the other so as to mix well the contents of both.
6. Repeat this movement several times.
7. Record the amount of gas remaining at the end of this procedure.
8. Test the residue of air with a burning splint.
9. Repeat the experiment twice replacing the air by nitrogen and by oxygen.
Observations
Photo
3: The amount of gas remaining
at the end of the procedure is 38 ml.
A burning splint dipped into a cylinder of a 20-ml syringe with air continues
to burn.
The burning splint is extinguished whe the air in this cylinder is replaced
by the residue of air left in the experiment.
Pure oxygen is totally consumed by the chemical reaction with the heat cells.
No reaction with nitrogen.
Explanation
The
oxygen of the air was consumed by a redox reaction with the ThermaCare ingredients.
The remaining gas is nitrogen.
The ingredients of ThermaCare®
are descibed under FAQs:
"Iron
reacts with oxygen in the air to provide heat in a process called iron oxidation.
* Sodium chloride (salt) speeds up the rate of reaction between iron and oxygen.
* Sodium thiosulfate controls hydrogen generation. * Water also is necessary
for the iron oxidation reaction. * Charcoal allows the iron powder to have
a surface to react inside the heat discs. The surface of this charcoal has
been treated (activated) to have special properties. * Sodium polyacrylate
controls the level of water present in the heat cell."