Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
potassium bromide : KBr
potassium bromate : KBrO3
calcium carbide : CaC2
Class:
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elem=C,Br
addition
redox
Summary:
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Bromine reacts with acetylene gas. The bromine disappears and a compound
is formed with a peculiar sweetish smell.
Description:
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Prepare a solution of potassium bromate and potassium bromide and add a large
excess amount of dilute sulphuric acid (appr. 0.3 mol/l): A strongly acidic
liquid is formed, with some bromine in it and above the liquid a fairly
thick orange/brown vapor of bromine can be observed.
Throw a small piece of 'carbid' (a very coarse technical quality of calcium
carbide, mainly impure due to carbon and traces of phosphide) in the liquid:
At the solid, a gas is evolved at fairly high speed. The orange/brown vapor
of bromine decolorizes fairly quickly and a white fume/smoke is formed
instead. It takes a little longer before the liquid has lost its bromine-
color. When a little of the fume is allowed to escape from the bottle, then
a sweetish smell can be observed, together with the familiar smell of the
gas mixture, produced by adding 'carbid' to water.
When the liquid is poured away and some water is added to the bottle containing
the white fumes, then with some shaking it is easy to dissolve the fumes in
the water. The water remains clear and colorless.