Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
vanadyl sulfate : VOSO4.5H2O
sodium persulfate : Na2S2O8
oxone : K2SO4.KHSO4.2KHSO5
Class:
------
elem=O,V
redox
Summary:
--------
The blue vanadyl ion VO(2+), which contains vanadium in oxidation state +4, is
oxidized by oxone (which contains the monopersulfate ion, SO5(2-)) and it also
is oxidized by the peroxodisulfate ion S2O8(2-). Oxidation by monopersulfate is
immediate, oxidation by peroxodisulfate is very slow. The latter reaction can
be sped up by heating, but still it takes tens of seconds on near boiling of
the solution.
The blue vanadyl ion is oxidized to the pale yellow pervanadyl ion VO2(+). On
heating, this pervanadyl ion condenses into more intensely colored ions which
contain multiple VO2(+) units. At a certain point the condensation of the
pervanadyl ions goes so far that a red/orange precipitate is formed of hydrous
vanadium pentaoxide, V2O5.nH2O.
Description:
------------
Add a solution of oxone to a solution of vanadyl sulfate: The liquid turns pale
yellow immediately. The pale yellow color is due to the presence of pervanadyl
ion.
Heat the pale yellow solution: The color of the liquid intensifies. The color
first becomes intense yellow, then it turns orange. At a certain point, when
the liquid is near boiling, a red/orange/brown precipitate is formed. This
precipitate quickly becomes coarser and settles at the bottom. The precipitate
is hydrous vanadium pentaoxide, V2O5.nH2O. The liquid above the precipitate is
very pale yellow, due to the presence of a very low concentration of condensed
pervanadyl ions.
----------------------------------------------------------------
Add a solution of sodium peroxodisulfate to a solution of vanadyl sulfate: No
visible reaction occurs. The liquid remains blue.
Heat the liquid to boiling: When the liquid is near boiling, then its color
slowly shifts from blue to green to olive green and then yellow green. At the
same time, the liquid turns turbid. On continued heating, the liquid turns
turbid more and more and the color shifts to orange/red/brown. Finally, a clump
of solid red/brown material settles at the bottom and a very pale yellow liquid
is above the solid. The end result is precisely the same as in the experiment
with oxone.
------------------------------------------------------------------
Add a solution of sodium peroxodisulfate to a solution of vanadyl sulfate: No
visible reaction occurs. The liquid remains blue.
Add a solution of oxone: Immediately the liquid turns pale yellow, due to
formation of pervanadyl ions.
Heat the liquid to boiling: Just like in the previous experiments, a brown/red
precipitate of hydrous vanadium pentoxide is formed.