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The Oxidation States of Vanadium

The Oxidation States of Vanadium. Objectives: Access multiple oxidation states of vanadium 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-. Hydrated Vanadium Complexes.

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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 vanadium Separate compounds via ion exchange chromatography

  2. Vanadium Complexes in This Lab • [V(H2O)6]2+ • [V(H2O)6]3+ • [V(H2O)5O]2+ • [V(OH)O3]2-

  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 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. Separation of ions • Ion exchange chromatography • SO32- ions attached to column • Most highly positively charged 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

  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. Summary --Synthesize vanadium compounds in four different oxidation states --Separate products by ion exchange chromatography --Determine concentrations of vanadium compounds

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