Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydroxyl amine sulfate : (NH3OH)2 SO4
hydroxyl amine hydrochloride : NH2OH.HCl
potassium bromate : KBrO3
sodium bromate : NaBrO3
Class:
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elem=N,Br
redox
Summary:
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Hydroxyl ammonium ion and bromate ion react with each other, but with a delay.
Once the reaction starts, it is EXTREMELY violent.
Description:
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Prepare a fairly concentrated solution of hydroxyl amine hydrochloride,
NH2OH.HCl. A small quantity in a test tube (e.g. 1 ml) is sufficient.
Add a small quantity (e.g. a volume of at most 4x4x3 mm3) of solid sodium
bromate to the concentrated solution: No reaction seems to occur, the solid
sodium bromate sits at the bottom of the test tube. After a while (at most a
few tens of seconds), there is a sudden explosion, followed by a very violent
decomposition reaction of the solution. The gas mix above the liquid becomes
light brown, due to formation of some NO2 (not Br2). The liquid remains
colorless and becomes very hot.
Add a little more solid sodium bromate to the very hot liquid: As soon as the
solid touches the liquid, a very violent reaction occurs and when sufficient
bromate is added, then at a certain point a lot of bromine vapor is produced.
Reaching of this point can be recognized easily, the light brown color of the
gas mix produced in the initial part of the experiment is replaced by a very
dense deep brown/red vapor and the liquid turns deep red/orange.
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Prepare a saturated solution of hydroxyl ammonium sulfate, (NH3OH)2SO4. Pour
1 ml of this solution into a test tube.
Add a small quantity of solid sodium bromate to this saturated solution: Just
as with NH2OH.HCl, there is a delayed reaction. It takes a somewhat longer
time before the reaction starts, compared to the reaction with NH2OH.HCl. The
reaction is very violent, but not explosive. It might be that the reaction is
somewhat less violent, because of the lower concentration of the hydroxyl
ammonium ion which can be obtained with the sulfate salt (it is less soluble).
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Repeat the experiment with NH2OH.HCl with KBrO3 instead of NaBrO3: When this
is done, then there is a delayed and violent reaction, but it is not an
explosive reaction. Probably this is due to the lower solubility of KBrO3.
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Warning: Do NOT scale up this experiment, use only a few hundreds of mg of
hydroxyl amine hydrochloride, dissolved in a small amount of water and use
appr. 50 mg of sodium bromate. Keep the test tube pointed away from persons,
some liquid may erupt out of the test tube due to the explosion.