Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium hydroxide : NaOH
ammonium chloride : NH4Cl
sodium persulfate : Na2S2O8
ammonium persulfate : (NH4)2S2O8
Class:
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elem=S;O
acid/base
redox
Summary:
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Persulfate decomposes in strongly alkaline environments.
Description:
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Three experiments are performed in order to get insight in the behavior
of persulfates when treated with hydroxide.
Experiment 1: Add solid NaOH to wet ammonium persulfate
Experiment 2: Add solid NaOH to wet sodium persulfate
Experiment 3: Add solid NaOH to wet ammonium chloride
In all three experiments some of the chemical to be treated with NaOH was
wetted with a few drops of water, such that a little slurry was made of
the chemical and the water. Solid NaOH was added to the white slurry.
Result of experiment 1: Vigorous reaction, the slurry turns pale yellow
during the reaction. Some heat is produced and a lot of gas is produced.
After the reaction has ceased, the yellow color has disappeared and the
slurry is white again. An odour of ammonia can be observed, but it is
not very strong (a 5% solution of NH3 in water has a much stronger smell
of NH3).
Result of experiment 2: Vigorous reaction, but not immediately after adding
the NaOH. It takes approximately 30 seconds before the reaction takes off.
During the vigorous reaction the slurry has a pale yellow color, which
disappears when the reaction ceases. No smell of ammonia, the evolved gas
is odourless. During the vigorous reaction some heat is produced.
Result of experiment 3: Vigorous reaction, which starts quickly after the
NaOH has been added. A lot of heat is produced. A lot of gas is evolved
and an unbearable suffocating odour of NH3 is produced. During the reaction
the slurry remains white.
The results of these experiments show that the persulfate ion decomposes
when a lot of hydroxide is added. The pale yellow color during the
reaction appears to be specific for the persulfate. Such a color is not
observed when ammonium chloride reacts with NaOH.