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electronic configuration and
origin of colour

4 types of reaction

tests for cations with
NaOH(aq) and NH3(aq)

specialised terms  and nomenclature

chemistry of copper complexes

occurrence and uses
of complexes

3 categories of catalysis

chromium complexes

redox aspects of complexes

vanadium redox chemistry

stereoisomers of complexes

chemistry of
other complexes

examination questions

The very colourful redox chemistry of vanadium.

Vanadium Redox Chemistry.

V 2+V 3+VO 2+VO2 +
+2

+3

+4+5

Reduction of VO2 + to V 2+ using granulated zinc metal in acid.

The following half-equations are required to explain the steps involved:

  1. VO2 + (aq)  +  2H + (aq)  +  e –  ⇌  VO 2+ (aq)  +  H2O (l)  EΘ =  + 1.00 V
  2. VO 2+ (aq)  +  2H + (aq)  +  e –  ⇌  V 3+ (aq)  +  H2O (l)     EΘ =  + 0.34 V
  3.  V 3+ (aq)   +  e –  ⇌  V 2+ (aq)                                                   EΘ =  – 0.26 V
  • Zn 2+ (aq)   +  2e –  ⇌  Zn (s)                                                   EΘ =  – 0.76 V
  • Sn 2+ (aq)   +  2e –  ⇌  Sn (s)                                                   EΘ =  – 0.14 V

Explain why an acidified solution of VO2 + turns from yellow:

  • to violet when an excess of zinc metal is added
  • to green when an excess of tin metal is added

     ACRONYM for the colours
 Very   –   Good   –   Being  –   Young
 Violet  – Green  –   Blue    –   Yellow
  V 2+ (aq)   V 3+ (aq)  VO 2+ (aq)  VO2 + (aq)
  +2         +3           +4              +5

Consider adding excess zinc to a solution of VO2 + in acid.

  • The Zn 2+ half cell has a lower reduction potential than VO2 +
  • 2VO2 + +  Zn → 2VO 2+ + Zn 2+
    Colour of the solution turns from yellow to blue
  • The Zn 2+ half cell also has a lower EΘ than VO 2+
  • 2VO 2+ +  Zn → 2V 3+ + Zn 2+
    Colour of the solution turns from blue to green
  • The Zn 2+ half cell also has a lower EΘ than V 3+
  • 2V 3+ +  Zn → 2V 2+ + Zn 2+
    Colour of the solution turns from green to violet

NOTE: Sn 2+ has a lower EΘ than both VO2 + and V 3+, but a lower EΘ than V 2+. The colour of the solution goes from Yellow  →  Blue  →  Green.

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