Redox Chemistry of Transition Metals

Reactions of the transition metals Iron, Manganese, Vanadium, Chromium and Cobalt required for A2 AQA Chemistry

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  • Created by: Jo Conway
  • Created on: 13-04-12 15:04

Iron

Iron exists is 2 states, Fe2+ and Fe3+

Fe2+ is oxidised easily in aqueous solutions:

Fe2+ àFe3+ + e-

This means Fe2+ is a reducing agent.

The concentration of Fe3+ is a solution can be determined by titrating with an oxidising agent.

 

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Manganese

Manganese exists commonly as Mn2+, Mn4+ and MnO4-, 

MnO4- can be reduced to Mn2+ by Fe2+ in acidified conditions:

8H+ + 5e- + MnO4- à Mn2+ +4H2O
Fe2+   
àFe3+ + e-

8H+ + 5 Fe2+ + MnO4- --> Mn2+ + 4 H2O + 5 Fe3+

 

 

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Vanadium

Vanadium exists in 4 common ions in aqueous solution: VO2+ VO2+ V3+ V2+

All vanadium compounds can be reduced to the +4, +3 and then +2 oxidation state by strong reducing agents such as zinc in acid solution:

 VO2+(aq) + 4H+(aq) + 3e- --> V2+(aq) + 2H2O(l)
Zn(s) --> Zn2+(aq) + 2e

2VO2+(aq) + 8H+(aq) + 3Zn(s) --> 2V2+(aq) + 3Zn2+(aq) + 4H2O(l) 

The colours of this reaction are:

yellow(VO2+) --> green (VO2+ and VO2+) --> blue (VO2+) --> green (V3+) --> violet (V2+)

Mild oxidising agents can reduce V5+ to V4+ but no further.
Air slowly oxidises V2+ to V3+ 

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