Derivatives of Pentapositive Vanadium

Like the metals of Groups IVa and Via, vanadium and its congeners display remarkable passivity unless finely divided. Thus, tantalum metal, although potentiometrically a better reducing agent than zinc metal, is almost inert to all mineral acids is practically unaffected by pure bromine or chlorine and is dissolved readily only by a mixture of HNOs and HF. The passivity of tantalum has made it useful for corrosion-resistant chemical equipment and for surgical wire that remains for extended periods of time within the body. Niobium is somewhat less resistant but is important as an additive to chromium steels. 

Vanadium(V) oxide, V2O5, a yellow, amphoteric solid, may be obtained as an intermediate in the preparation of vanadium metal, as indi- 

The thiovanadate ion, VS73, resembles the permanganate ion in color. Like the latter, it is one of the few deeply colored ions known in which there are no partially-filled d subshells. 

The +4, +3, and +2 states of vanadium may be obtained by stepwise reduction of pentapositive vanadium, using successively stronger reducing agents  

Halides and oxides corresponding to each of the states are known but will not be described here. The lower oxidation states of vanadium are summarized in Table 26-2. 

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