The oxidation states of vanadium

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The oxidation states of vanadium

• Objectives
• access multiple oxidation states of V
• separate compounds via ion exchange chromatography

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Vanadium Complexes in This Lab

• V(H2O)62
• V(H2O)63
• V(H2O)5O2
• V(OH)O32-
• Draw 3D structure
• Give oxidation number of V

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Hydrated Vanadium Complexes
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Reduction of vanadium

• 5 ? 4 HCl (done in hood!)
• 4 ? 3 Hg/Zn amalgam
• 3 ? 2 Hg/Zn amalgam

• Reaction with amalgam may occur faster than
• expected do not overdo shaking!

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Standard reduction potentials (half reactions,
acid)

• Reaction E0 (V)
• 5?4 VO3- 4H e- ? VO2 2H2O 1.00
• 4?3 VO2 2H e- ? V3(aq) H2O 0.34
• 3?2 V3(aq) e- ? V2(aq) -0.26

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Two couples are needed for determining potential
Reaction E0 (V) 5 ? 4 VO3 4H e ?
VO2 2H2O 1.00 4 ? 3 VO2 2H e ?
V3(aq) H2O 0.34 3 ? 2 V3(aq) e ?
V2(aq) -0.26 Cl2 2e
? 2Cl 1.36 Zn2 2e ? Zn(Hg)
-0.76
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Redox chemistry of vanadium (Latimer)

• Values for acidic solution (pH 0)
• DG0 -nFE0
• n mol e-
• F 96,500 C / mol e-
• E0 standard reduction potential in V (1M conc,
  1 atm pressure)
• 1 Joule (1 Volt)(1 Coulomb)

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Oxidation of vanadium

• Oxidizing agent KMnO4
• MnO4- 8H 5e- ------gt Mn2 4 H2O 1.52 V
• Why is KMnO4 a good oxidizing agent?

--show oxidations with KMnO4 stepwise
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Separation of ions

• Ion exchange chromatography

• SO32- ions attached to column

• Positive ions travel more slowly through column

resin

• Can adjust rate via competitive binding

• Resin must be kept wet to avoid cracking
• Resin must have sufficient height to achieve
  separation
• Unsettled height is 3X greater than settled
  height