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The brown ring complex compound has the formula [Fe(H2O)5(NO)]SO4. Determine the oxidation state of iron in this complex.
- +1
- +2
- +3
- 0
Correct answer: +1
Solution
In [Fe(H2O)5(NO)]SO4, the sulphate ion SO4²- requires the complex cation to carry a +2 charge. Water is neutral. NO here is a 3-electron donor acting formally as NO+. So: Fe oxidation state + charge of NO+ = +2. If NO is NO+ (charge +1): Fe + 1 = 2, so Fe = +1. This is the accepted answer: Fe is in the +1 oxidation state in this classic brown ring complex.
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