Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
sodium biphosphate : NaH2PO4 . H2O
vanadyl sulfate : VOSO4.5H2O
Class:
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elem=V,P
precipitation
Summary:
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Vanadyl forms a light blue or white compound with phosphates, when it is
precipitated.
In excess alkali, this dissolves, forming a greenish brown clear liquid.
This color is like the familiar brown color of strongly alkaline solutions,
containing vanadium in the +4 oxidation state, but a little bit less reddish
and more greenish.
Description:
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Add a solution of sodium biphosphate to an acidic solution of vanadyl sulfate:
No visible reaction, the liquid becomes sky-blue.
Add a solution of sodium hydroxide to the sky-blue liquid, in small amounts:
When the first amount is added, a light blue precipitate is formed. When more
is added, the precipitate looks a little lighter and thicker. The liquid
becomes turbid and very light blue. It is not clear, whether this is the
color of the precipitate or due to excess free vanadyl.
When even more solution of sodium hydroxide is added, then the liquid remains
turbid, but the color shifts a little towards green.
Ann adding yet more solution of sodium hydroxide, the precipitate dissolves
and the liquid becomes brown, with a faint greenish hue.