3.2.5.5: Variable Oxidation States

• Vanadium Chemistry:

  • A - V2+
  • B - V3+
  • C - VO 2+
  • D - VO2 +
  • E - +2
  • F - +3
  • G - +4
  • H - +5

  
• • Vanadium's oxidation state changes from: 5+ to 4+
  • The colour change that occurs is: yellow to blue

  
• • Vanadium's oxidation state changes from: 4+ to 3+
  • The colour change that occurs is: blue to green

  
• • Vanadium's oxidation state changes from: 3+ to 2+
  • The colour change that occurs is: green to violet

  
• Redox Potentials

  • Larger ( more +ve) redox potential -> eqm. lies to the right  ∴ species more easily reduced  ∴ better oxidising agent
  • Smaller (more -ve) redox potential -> eqm. lies to left  ∴ species more easily oxidised  ∴ better reducing agent
  • Done in STANDARD CONDITIONS: 298K, 100kPa, [ions] at 1 mol / dm^3
• Two factors that affect (the size of) redox potentials:

  • pH
  • type of ligand
• Ligands in Redox Potentials

  • ϵ always calculated in AQUEOUS SOLUTIONS (metal ion surrounded by water molecules)
  • certain ligands other than H2O form stronger bonds with different oxidation states -> redox potential changes from standard value
• pH in Redox Potentials

  • More acidic solution -> ion more easily reduced (better oxidising agent) -> favours reduction -> eqm. lies to the right
  • More basic/alkaline solution - ion more easily oxidised -> favours oxidation -> eqm. lies to the left
  • Larger, more +ve ϵ value -> eqm. lies to right -> favours reduction of metal
  • Smaller, more -ve value -> eqm. lies to left -> favours oxidation of metal