Description of experiment
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Needed compounds:
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nitric acid : HNO3
ammonia : NH3
sodium hydroxide : NaOH
hydroxyl amine sulfate : (NH3OH)2 SO4
silver nitrate : AgNO3
Class:
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elem=Ag,N
redox
precipitation
Summary:
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Silver (I) is not reduced by hydroxyl amine in neutral environments. When
made alkaline, it is reduced to metallic silver immediately.
Description:
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Dissolve some silver nitrate in distilled water and add some solid hydroxyl
amine sulfate: The hydroxyl amine sulfate quickly dissolves, but a new solid
is formed quickly. A heavy white precipitate appears. Probably the white
precipitate is silver sulfate, which is only sparingly soluble in water.
The white precipitate quickly sinks to the bottom after shaking, leaving
a colorless and clear liquid above it.
Decant the colorless and clear liquid from the precipitate and add this clear
liquid to a solution of NaOH: As soon as the liquids touch each other, a
black precipitate is formed. The black particles tend to stick to each other
and two large black pieces of porous precipitated silver are formed.
Rinse the white precipitate with distilled water a few times and then add
excess ammonia (5% by weight) to the white precipitate: The white precipitate
immediately dissolves. The liquid becomes almost clear and colorless. It is
not fully clear, probably rinsing was not complete and some hydroxyl amine
remained, which reduces a small part of the silver (I) to metallic silver.
The color of the turbidity was greyish and is ascribed to finely dispersed
metallic silver.
Add some nitric acid (52% HNO3 by weight) to the two porous black pieces: The
black pieces quickly dissolve and some gas is evolved. The gas mixture above
the acid liquid becomes pale brown.