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General : Vanadium- URGENT
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 Message 1 of 3 in Discussion 
From: MSN NicknameAlbert1145  (Original Message)Sent: 8/14/2008 1:16 PM
Hi, I'm having a bit of problem

In alkaline solution V(V) occurs as the oxoion VO4 3-. In acidic solution V(V) occurs as the oxoion VO2+. Addition of hydrogen peroxide to an acidic solution of VO2+ results in formation of the mono peroxo vanadium(V) ion, [V(O2)O]+. this species is charged and therefore soluble in water. It is not soluble in organic solvents.

So... my problems are I can't figure out what I would get in the following reagents:

V(V) + NaOH (initially) = is it VO4 3-?
V(V) + Na OH (excess) = VO4 3-??
V(V) + NaOH + H2O2 = I have no idea
V(V) + H + H2O2 = I'm guessing [V(O2)O]+

Could you help me?
Thanx


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Reply
 Message 2 of 3 in Discussion 
From: MSN Nickname·Steve·Sent: 8/15/2008 3:47 AM
According to my Cotton & Wilkinson, the chemistry of the vanadates is very complicated.  It says that vanadium(V) oxide, V2O5, dissolves in sodium hydroxide to give colorless solutions which consist mainly of the VO43�?/SUP> ion at pH 13 and above.  As the pH is lowered, the solution contains various species which change as the pH is lowered.  At about pH 3 and lower, a major species is the VO2+ ion (still vanadium(V)).

When hydrogen peroxide is added to acidic (I wonder if this should be basic, see below*) vanadium(V) solutions, a red color is formed which results from peroxo complexes in which oxygen atoms in VO43�?/SUP> are replaced by one or more O22�?/SUP> groups.  Several of these peroxovanadates have been isolated, including a complex of the V(O2)3�?/SUP> ion.  The monoperoxovanadium(V) species, according to this, would have the formula V(O2)O33�?/SUP> (replacing one oxide ion in VO43�?/SUP> with the peroxide ion O22�?/SUP>), but it was not mentioned in Cotton & Wilkinson.  Nor was the ion you mentioned, V(O2)O+.
 
*This might be an error in Cotton & Wilkinson, unlikely as that is.  But if we go with the assumption that hydrogen peroxide results in replacing oxide ions one at a time with peroxide ions to the vanadium(V) species that is predominant in strongly basic and strongly acidic solution, then we have:

Basic Solution
VO43�?/SUP> (aq)  +  H2O2 (aq)   ––�?gt;   V(O2)O33�?/SUP> (aq)  +  H2O (l)

Acidic Solution
VO2+ (aq)  +  H2O2 (aq)   ––�?gt;   V(O2)O+ (aq)  +  H2O (l)

Reply
 Message 3 of 3 in Discussion 
From: MSN NicknameAlbert1145Sent: 8/18/2008 1:27 PM
Thanx for your explanation