Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
sulphuric acid : H2SO4
sodium sulfide : Na2S . 3H2O
ammonia : NH3
vanadium pentoxide : V2O5
Class:
------
elem=V,S
coordination
Summary:
--------
Sulfide reacts with metavanadates, resulting in the formation of a dark
brown/greenish compound.
Description:
------------
Add some vanadium pentoxide to ammonia (5% by weight): The solid dissolves,
the liquid becomes yellow. Part of the solid becomes covered by a greyish
compound and does not (or at a very slow rate) dissolve.
Heat until liquid starts boiling: The remaining part of the solid dissolves,
the liquid almost becomes colorless.
Add some solid sodium sulfide to the still hot solution: The solid dissolves
and the liquid becomes dark (almost black) brown/green. The liquid appears
to be clear, but because of the dark color it may be that it contains very
small solid particles. If there is a precipitate, then it is an extremely
finely divided precipitate.
Prepare a very dilute solution of sulphuric acid (just a few tenths of
percent) and add a few drops of the dark solution to the dilute aced. A
large excess amount of dilute acid is used: The resulting liquid becomes
light yellow and a little turbid. A faint odour of hydrogen sulfide is
observed.
Slowly add some of the strongly diluted sulphuric acid to the dark brown/
green liquid: No clear visible changes are observed.