Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium hydroxide : NaOH
potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
hydroxyl amine sulfate : (NH3OH)2 SO4
Class:
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elem=Fe
redox
Summary:
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Hydroxyl amine reacts with ferrocyanides, forming a dark compound. Is the
ferrocyanide oxidized by the hydroxyl amine? This reaction occurs in
neutral environments, with the hydroxyl amine bound in a hydroxyl ammonium
salt.
Description:
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Add a solution of hydroxyl amine sulfate to a solution of potassium
ferrocyanide: Initially, the liquid is almost colorless. On heating, however,
the liquid becomes yellow. When the liquid is boiled gently, it further
changes from yellow to green. Finally, the liquid is dark green.
Let the liquid stand without disturbances for a few days: Formation of a dark
blue precipitate and a clear dark green liquid is above the precipitate.
Split liquid and precipitate and add an excess amount of NaOH to both the
liquid and the precipitate:
- The precipitate becomes light brown, it does not dissolve.
- The liquid becomes yellow/green and a little turbid
Add an excess amount of HCl (appr. 10% by weight) to the yellow/green turbid
liquid: The liquid becomes dark green and clear again.