Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrogen peroxide : H2O2
sodium hydroxide : NaOH
ferrous ammonium sulfate hexa hydrate : Fe (NH4)2 (SO4)2 . 6H2O
Class:
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elem=Fe
redox
Summary:
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Ferrous ions react with hydroxide, forming a light bluish/grey precipitate.
This precipitate, however, quickly turns brown.
Description:
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Sequence 1:
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Dissolve some ferrous ammonium sulfate in water, that has been boiled for a
while and cooled down again (the boiling is for expelling oxygen from the
water): The liquid becomes clear and colorless. The color of hydrated Fe2+
is so pale, that it cannot be observed in a testtube of just over 1 cm
thickness.
Dissolve some sodium hydroxide in distilled water, that has been boiled for
a while and cooled down again: A clear solution is obtained.
Mix both solutions: A light grey/blue/green precipitate is formed. At the
surface of the liquid, it quickly turns rusty brown.
Let liquid with precipitate stand for a few days: After a few days, the
precipitate has settled. At the bottom there is a light green/blue precipitate,
covered by a layer of rusty red/brown. The liquid above the precipitate is
clear and colorless.
Oxygen from the air slowly penetrates deeper into the precipitate, oxydizing
all ferrous precipitate to ferric precipitate.
Sequence 2:
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Dissolve some ferrous ammonium sulfate in water, that has been boiled for a
while and cooled down again (the boiling is for expelling oxygen from the
water): The liquid becomes clear and colorless. The color of hydrated Fe2+
is so pale, that it cannot be observed in a testtube of just over 1 cm
thickness.
Dissolve some sodium hydroxide in distilled water, that has been boiled for
a while and cooled down again: A clear solution is obtained.
Mix both solutions: A light grey/blue/green precipitate is formed. At the
surface of the liquid, it quickly turns rusty brown.
Add a few drops of 10% H2O2 and shake: The precipitate in the entire liquid
at once turns rusty brown. No gas is evolved.