Mystery 'Cakey' red precipitate structure formed in vanadium practical

[Jeannette98]

I am a first year undergraduate and in my inorganic module we have recently undertaken a practical to find out various oxidation states of Vanadium. To start we made a stock solution by dissolving 2g of ammonium metavanadate (V) with 1.0 mol.dm^-3 20 cm³ of sodium hydroxide. This we then added 35.0 cm³  sulphuric acid (1.0  mol.dm^-3 ) and made the volume up to 250cm³  with deionised water. It was after the addition of the sulphuric acid that we observed the yellow solution and a red/brown precipitate/solid that then settled to the bottom of the volumetric flask. The solution was meant to be yellow with none of this precipitate so our initial thoughts are that a salt has been formed but to no avail have we found out what it is. Does anyone have any ideas of what was formed?

Thank you in advance !

[John Cuthber]

Vanadium pentoxide is red and not very soluble in water.

[Fuzzwood]

Metavanadate can only exist in basic solutions. Trying to make vanadyl sulphate is a tricky process.