Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrogen peroxide : H2O2
sulphuric acid : H2SO4
sodium dithionite : Na2S2O4 . 2H2O
sodium hydroxide : NaOH
ammonium molybdate : (NH4)6Mo7O24 . 4H2O
Class:
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elem=Mo
redox
Summary:
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In strongly alkaline environments, molybdates are not as easily reduced
as in neutral or acidic environments.
Description:
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Add solid sodium hydroxide and solid ammonium molybdate to some water:
Both solids dissolve and the liquid becomes clear and colorless.
Add a small quantity of sodium dithionite: The solid dissolves. The liquid
remains colorless.
Add an excess amount of H2SO4 (appr. 20% by weight), such that all NaOH is
neutralized and acid remains: The liquid turns intense blue.
Add an excess amount of H2O2 (3%): Liquid turns pale yellow.
Add a large amount of sodium dithionite: Formation of H2S (smell), bubbling
on the crystals of sodium dithionite (O2 or H2S ???). Liquid turns turbid
and brown.