Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
potassium ferricyanide : K3 [Fe(CN)6]
sodium thiosulfate : Na2S2O3 . 5H2O
ammonium persulfate : (NH4)2S2O8
silver nitrate : AgNO3
sodium hydroxide : NaOH
sodium sulfite : Na2SO3
metol : (CH3 NH C6H4 OH)2 . H2SO4
Class:
------
elem=C,Ag
redox
photo
Summary:
--------
Silver (I) is reduced to metallic silver by metol. This metallic silver
is easily oxidized by peroxosulfate.
Insoluble silver (I) compounds dissolve in thiosulfate solutions (principle
of photography fixer) while metallic silver is not affected.
When a mild oxidizer is added, the metallic silver also dissolves (principle
of photography reducer, Farmer's reducer).
Description:
------------
Add a solution of AgNO3 to a solution of metol/NaOH/Na2SO3 (metol in alkaline
solution, protected by sulfite): Immediate formation of a black precipitate.
This black precipitate is metallic silver.
Let precipitate settle and remove liquid.
Add some tap water to the black precipitate (tap water contains chloride and
other compounds) and add some ammonium peroxosulfate: The ammonium
peroxosulfate dissolves and part of the silver also dissolves. The liquid
becomes slightly turbid (formation of AgCl).
Add some solid Na2S2O3.5H2O: The solid dissolves and the liquid becomes
clear again. The black silver does not dissolve.
Add some solid K3Fe(CN)6: The solid dissolves, the silver now also dissolves
quickly. The liquid becomes yellow and clear.