Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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ammonia : NH3
sodium sulfite : Na2SO3
hydrochloric acid : HCl
sodium bromate : NaBrO3
tetraethyl ammonium bromide : (CH3CH2)4NBr
Class:
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elem=C,N
organic
Summary:
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Tetraethyl ammonium ion does not form a sparingly soluble salt with bromate
ion.
The tetraethyl ammonium ion forms an oily compound, when treated with
bromate and hydrochloric acid. The halogen, released in that reaction
apparently forms a liquid organic, insoluble in water, or is a liquid
ionic compound formed, some tetraethyl ammonium polyhalogenide compound???
There is evidence for the latter (see experiment detailed description).
Description:
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Dissolve some tetraethylammonium bromide in water and add a concentrated
solution of NaBrO3: No visible reaction, no formation of a precipitate or
slow separation of crystals. Hence, it may be assumed that tetraethylammonium
bromate is soluble quite well in water.
Add some concentrated hydrochloric acid: Formation of a mix of chlorine and
bromine gas (mainly chlorine) and the liquid becomes turbid. Quickly, orange
droplets of an oily and dense substance settle at the bottom. After some
time, there is a single big blob of an oily substance on the bottom, and
the surface of the liquid also is covered by some oily substance. The aqueous
phase is yellow, due to a mix of chlorine and bromine.
Add a lot of water, decant and add a lot of water again: The oily drop remains
orange, it looks as if the oily drop slowly releases chlorine and/or bromine
to the water, near the oily drop, the liquid is yellow, while further away
the liquid is colorless. The oily drop has a strong pungent smell of chlorine.
Wait for a few hours: Around the drop, the liquid is orange/yellow.
Decant most of the water, and add some sodium sulfite: At the oily liquid,
a gas is formed, which bubbles upwards, but the gas does not reach the
surface. Before the bubbles reach the surface, they dissolve in the liquid.
Most likely this gas is sulphur dioxide, formed in a reaction.
While the gas is formed, the oily droplet becomes darker, until it becomes
brick-red. The drop also slowly solidifies and a few minutes after adding
the sodium sulfite, the orange drop is replaced by a brick-red solid
particle, just a little bit smaller than the initial oily drop.
Take the solid piece out of the liquid and rinse with some water: The solid
piece does not dissolve. The brick-red solid has a strong and pungent smell
of bromine, although no bromine vapor can be seen. The bromine vapor only
can be observed through its smell.
Add the solid to some dilute ammonia (appr. 2% NH3 by weight): The piece
slowly dissolves, while a colorless gas is evolved, which does not dissolve
in the liquid. The entire piece finally dissolves (takes a few minutes)
and a colorless liquid remains.
Remark: It might well be possible that the oily drop is a mixture of
tetraethylammonium polyhalogenides (an ionic liquid), where the polyhalogenides
are chloro/bromo complexes. On addition of the sulfite, the chlorine-based
polyhalogenide is reduced, forming hydrogen chloride, sulphur dioxide and
tetraethylammonium monohalogenide, which all go into solution. What remains
is tetraethylammonium tribromide, which is the brick-red solid. On addition
of ammonia, the tribromide splits up in bromine and bromide, where the
bromine reacts with the ammonia, giving nitrogen gas, ammonium ion and bromide
ion. Finally all has dissolved, leaving tetraethylammonium bromide and
ammonium bromide in solution.