Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
hydroquinone : HO C6H4 OH
sodium hydroxide : NaOH
metol : (CH3 NH C6H4 OH)2 . H2SO4
potassium bromide : KBr
silver nitrate : AgNO3
Class:
------
elem=Ag,C
photography
precipitation
redox
Summary:
--------
Silver bromide is reduced by metol in alkaline medium.
Description:
------------
Add a solution of potassium bromide to a solution of silver nitrate:
Formation of a pale yellow (almost white) precipitate, which remains in
the liquid as small floating particles.
Add some metol and shake for a while: The solid metol slowly dissolves,
no further visible changes.
Add some solution of NaOH and shake well: The pale yellow precipitate
turns dark grey (almost black). The change of color is not momentaneous
but it takes approximately 10 seconds (at approximately 15 C). The liquid
itself becomes red/brown.
Add a small amount of hydroquinone and shake: The hydroquinone dissolves.
The liquid becomes very dark (almost black). The precipitate does not
change (it may have become slightly darker, but this can also be because
of the dark color of the liquid).