Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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metol : (CH3 NH C6H4 OH)2 . H2SO4
p-aminophenol HCl : NH2 C6H4 OH . HCl
sodium sulfite : Na2SO3
EDTA tetra sodium : (NaOOC CH2)2 N CH2 CH2 N (CH2 COONa)2
ferric chloride : FeCl3 . 6H2O
Class:
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elem=Fe
coordination
Summary:
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Although p-aminophenol and metol are similar compounds (metol is the
sulfate salt of p-aminophenol with a H-atom at the amino-group replaced
by a methyl group) they show fairly large differences as far as complex-
formation is concerned with ferric compounds.
Metol reacts more slowly and the color of the compounds differ.
Description:
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Add a solution of ferric chloride (acidified with a little amount of HCl in
order to keep it clear) to a solution of EDTA-Na4: The liquid turns red/brown
on first contact but a few seconds later it is yellow/brown. The red/brown
coloration may be due to precipitation of ferric hydroxide (hydrolysis in the
slightly alkaline EDTA-Na4) which redissolves again when more ferric chloride
solution is added.
This yellow/brown liquid is used for the remaining part of this experiment.
Sequence 1:
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Add a solution of p-aminophenol HCl to the brown/yellow solution: The liquid
becomes purple/blue. The change of color takes a few seconds, it is not
momentaneous. After appr. 1 day the liquid has becomes turbid. It looks as
if there are dark brown particles in a deep blue/purple liquid, but this
observation is not very certain, due to the darkness of the liquid.
Add an excess amount of sodium sulfite: The liquid becomes yellow and turbid.
The particles in the liquid are brown.
Sequence 2:
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Add a solution of metol to the brown/yellow solution: No clear change,
immediately after mixing the two liquids. The resulting liquid is just a
little bit more reddish than the original solution. After 1 hour, however,
the liquid has becomes deep red/purple. After appr. 1 day, the liquid has
become turbid, due to the presence of brown particles, which are floating
around in the liquid.
Add an excess amount of sodium sulfite: The liquid appears to become a
little bit lighter. The color of the liquid remains brown and the liquid
remains turbid.