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The oxidation states of vanadium

The oxidation states of vanadium. Objectives: access multiple oxidation states of V separate compounds via ion exchange chromatography. Vanadium Complexes in This Lab. [V(H 2 O)] 6 2+ [V(H 2 O) 6 ] 3+ [V(H 2 O) 5 O] 2+ [V(OH)O 3 ] 2- Draw 3D structure Give oxidation number of V.

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The oxidation states of vanadium

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  1. The oxidation states of vanadium Objectives: access multiple oxidation states of V separate compounds via ion exchange chromatography

  2. Vanadium Complexes in This Lab • [V(H2O)]62+ • [V(H2O)6]3+ • [V(H2O)5O]2+ • [V(OH)O3]2- • Draw 3D structure • Give oxidation number of V

  3. Hydrated Vanadium Complexes

  4. 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!

  5. 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

  6. Two couples are needed for determining potential Reaction E0 (V) 5+ → 4+ VO3ˉ + 4H+ + eˉ  VO2+ + 2H2O +1.00 4+ → 3+ VO2+ + 2H+ + eˉ V3+(aq) + H2O +0.34 3+ → 2+ V3+(aq) + eˉ V2+(aq) -0.26 Cl2 + 2eˉ 2Clˉ +1.36 Zn2+ + 2eˉ Zn(Hg) -0.76

  7. 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)

  8. Oxidation of vanadium • Oxidizing agent: KMnO4 MnO4- + 8H+ + 5e- ------> Mn2+ + 4 H2O 1.52 V Why is KMnO4a good oxidizing agent? --show oxidations with KMnO4 stepwise

  9. Separation of ions • Ion exchange chromatography • SO32- ions attached to column • Positive ions travel more slowly through column • Can adjust rate via competitive binding resin • Resin must be kept wet to avoid cracking • Resin must have sufficient height to achieve separation • Unsettled height is ~3X greater than settled height

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