Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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bleach : NaClO
sulphuric acid : H2SO4
phosphorus red : P
Class:
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elem=P,S
redox
Summary:
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Red phosphorus dissolves in concentrated sulphuric acid, when it is strongly
heated.
Description:
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Add a pinch of powdered red phosphorus to 2 ml of concentrated sulphuric acid
and shake: Nothing special happens. The solid is dispersed through the liquid,
but no reaction occurs.
Heat the liquid, until white fumes are produced (CAREFUL with such very hot
sulphuric acid, use a test tube which is guaranteed not to crack): The
particles of red phosphorus slowly dissolve, and a colorless gas is produced.
The gas is sulphur dioxide, its smell can be observed easily.
Most likely, the phosphorus is oxidized to P4O10 (or a derived acid thereof)
and the sulphuric acid is reduced to SO2 and H2O. Most of the red phosphorus
can be dissolved in this way, but a small amount of black solid material
remains. Even heating for somewhat longer time, such that the acid starts
boiling, does not result in the dissolving of these black particles.
Let the liquid cool down and then add 5 times its volume of 5% NaOCl solution:
The resulting liquid becomes hot, and a lot of chlorine gas is produced. The
remaining black particles now almost completely dissolve, only a few larger
particles remain. Probably, the larger particles also are phosphorus, but in a
somewhat less reactive form. The red phosphorus, used in this experiment, has
some glittering pieces, which are somewhat larger. This may be the cause of the
small amount of non-reacting (or slowly re