Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
sulphur : S8
potassium bromate : KBrO3
sulphuric acid : H2SO4
potassium bromide : KBr
Class:
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elem=Br,S
redox
Summary:
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A large amount of sulphur can be added to bromine, before a solid remains in
the liquid bromine. The sulphur dissolves in the bromine very easily.
Description:
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Dissolve some potassium bromide in a small volume of water and add sulphuric
acid to the liquid: A lot of heat is produced and the liquid becomes yellow/
orange. Apparently some bromine is formed. After a while, a solid crystalline
mass separates from the liquid, probably this is KHSO4 or K2SO4.
Decant liquid from the crystalline mass and add some solid KBrO3 to the clear
yellow/orange liquid: Formation of a lot of bromine, liquid becomes a little
warmer. Finally, all KBrO3 has dissolved and a large drop of bromine is at the
bottom of the test tube. The drop of bromine is dark brown.
Add solid sulphur in small amounts multiple times: The sulphur sinks to the
bottom of the liquid and finally touches the drop of bromine. As soon as the
sulphur touches the drop of bromine it disappears at once. It is absorbed by
the drop and it looks as if it completely dissolves. The drop remains liquid.
Quite a lot of sulphur can be added this way, before some solid sulphur
remains, which is covered totally by the drop of bromine.
Decant most of the liquid above the drop of bromine and pour the drop of
bromine in an erlenmeyer, filled with a lot of water. Decant the water and
replace with clean water: The drop remains at the bottom and very slowly
gives off some bromine to the water (water becomes yellow around the drop).
Add some solid NaOH and manouvre the solid (before it dissolves in the water),
such that it comes in contact with the large drop of bromine with sulphur: A
violent reaction occurs, as soon as the solid NaOH comes in contact with the
drop of bromine. A pale yellow solid is given off during this reaction and
ejected into the water. The water becomes turbid.
Add much more solid NaOH and assure that quite a lot of this is absorbed by
the dark brown drop: The drop is converted to a yellow solid (probably this
is sulphur) and a red liquid. Finally, the red liquid also is converted to
the pale yellow solid. Finally, a yellow lump remains, with small orange/red
particles in it. These orange/red particles do not disappear.
Add some HCl (appr. 30% by weight): The liquid becomes much more turbid milky
yellow/white. A faint smell of H2S can be observed. The lump of sulphur, with
the orange/red particles is not affected.
Decant the water: A faint odour of bromine can be observed.