Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
sodium hydroxide : NaOH
sodium chlorate : NaClO3
sodium biphosphate : NaH2PO4 . H2O
ammonium molybdate : (NH4)6Mo7O24 . 4H2O
Class:
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elem=Mo,P
coordination
Summary:
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Ammonium molybdate forms a yellow coordination complex with phosphates in
acidic environments, which precipitates. Oxidizing compounds do not
dissolve this precipitate, alkaline compounds do dissolve this precipitate.
Description:
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Sequence 1:
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Add a solution of ammonium molybdate in dilute H2SO (appr. 0.5 mol/l) to
some solid sodium biphosphate: The solid quickly dissolves and the liquid
becomes clear and colorless.
Heat the liquid and boil gently for a while: The liquid becomes yellow and
lateron a yellow precipitate is formed, which sticks at the glass.
Add some sodium chlorate and boil again: The precipitate does not change.
Decant the liquid and keep some of the precipitate. Add some solid NaOH and
shake: All of the precipitate quickly dissolves. The resulting liquid
becomes clear and colorless again.
Sequence 2:
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Add a solution of ammonium molybdate in dilute H2SO (appr. 0.5 mol/l) to
some solid sodium chlorate: The solid quickly dissolves and the liquid
becomes clear and colorless.
Heat the liquid and boil gently for a while: The liquid becomes very light
green (almost colorless) and remains clear. No precipitate is formed with
chlorate.