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oxidation states of vanadium

2 months 2 weeks ago #42108 by Doolally
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  • oxidation states of vanadium was created by Doolally
    Having trouble getting this practical to work.
    Method states - dissolve 1g ammonium metavanadate in 10ml 2M NaOH, add 20ml 1M sulfuric acid then "a few pieces" granulated zinc. Stopper the boiling tube, shake until no further changes occur, releasing pressure from time to time.

    It's been awhile since we last did this but going by my tech info sheet it looks like we swapped out the boiling tubes for 100ml flasks and the granulated zinc for zinc powder. Then it looks like we also put the flask in a hot water bath.

    I've been trying to get this to work but for a start I get an orange solution to begin with before adding the zinc when it should be yellow.
    Then I get green (like a dark olive green) but then it seems to go black.
    The only time I got to even blue was by adding more 1M sulfuric acid.
    But I've never got to the purple.

    I've seen YouTube videos but they never give concentrations of solutions or amounts of zinc added so aren't a great help.

    Anyone got any tips? Cheers :)

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    2 months 2 weeks ago #42109 by SteveKeys
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  • Replied by SteveKeys on topic oxidation states of vanadium
    My Recipe for the Metavanadate in this experiment is slightly different....

    "0.5g solid, dissolved in 1M H2SO4, then SLOWLY add conc H2SO4 with stirring until tyou get a clear yellow solution"

    My gut feeling is if your metavanadate isn't the right colour to start with, I wouldn't even look at the colours further down the line until this is sorted.

    Steve
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    2 months 1 week ago #42110 by Doolally
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  • Replied by Doolally on topic oxidation states of vanadium
    Thank you for that alternate method. Was trying to avoid using the conc acid with pupils 
    I found yet another method from the RSC online.
    Success!
    It's supposed to be a demo so I scaled it down.
    3.51g ammonium metavanadate in 270ml 1M sulfuric and 30ml deionised water.
    Yellow!!!
    30ml of this in a 100ml flask and add 0.9g zinc pdr.
    Goes green to blue and then leave it to stand for about half an hour and you get the mauve.
    It then suggests filtering off a little at this stage into a boiling tube and adding acidified KMnO4 dropwise carefully so as not to mask the colours as you take it back to the start.
    Going to try that when i get a good mauve.

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