Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium persulfate : Na2S2O8
sodium sulfide : Na2S . 3H2O
ferrous sulfate : FeSO4 . 7H2O
ascorbic acid : C6H8O6
stannous chloride : SnCl2
hydrochloric acid : HCl
sodium sulfite hepta hydrate : Na2SO3 . 7H2O
sodium chloride : NaCl
palladium chloride : PdCl2
Class:
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elem=Pd,S
redox
Summary:
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Palladium (II) is not easily reduced by mild reducing agents. Only very
strong reductors are capable of reducing this to metallic palladium.
Strong oxidizers probably are capable of oxidizing palladium (II) to a
higher oxidation state, but if this is true, then the higher oxidation
state has almost the same color.
Sulfite, instead of reducing palladium to the metallic state, appears to
form a brightly colored coordination complex in acidic environments.
Description:
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Prepare a solution of Na2PdCl4 by dissolving PdCl2 in excess solution of NaCl.
This liquid is called LIQPD.
Sequence 1:
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Add a solution of sodium sulfite to LIQPD: Formation of a light yellow
precipitate.
Add an excess amount of HCl (appr. 10% by weight): The yellow precipitate
dissolves, the liquid becomes yellow/green. There is a strong smell of SO2.
Heat the liquid and boil gently for a few minutes: All SO2 is driven off, no
smell of SO2 from the liquid anymore. The liquid becomes brown again and
remains clear.
Add one crystal of Na2SO3.7H2O: The crystal dissolves and the liquid becomes
yellow/green again and remains clear.
Add an excess amount of a solution of SnCl2 in 30% HCl: Formation of a brown
precipitate. Probably this is finely divided elementary Pd.
Sequence 2:
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Add a solution of ascorbic acid in 10% HCl to LIQPD: No visible changes.
Boil gently for a while: No visible reaction.
Add a solution of ferrous sulfate: No visible reaction.
Add a solution of sodium sulfide: Formation of a darkbrown precipitate. This
must be Pd. It cannot be FeS, because that does not form a precipitate at the
low pH of the liquid.
Sequence 3:
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Add some solid Na2S2O8 to LIQPD: The solid dissolves, no further visible
changes.
Boil the liquid gently: Liquid becomes darker, the color remains brown.
However, the color shifts towards red.