Analytical Chemistry of Iron

The standard reduction potential of iron (III) /(II) in acid solution is  

For any redox couple whose E° is appreciably more positive, the oxidant will oxidise Fe(II) to Fe(III) and for couples whose E is less positive, or negative, the reductant of the couple will reduce Fe(III) to Fe(II). However, E for Fe(III)/Fe(II) changes when the ions are complexed or when die solutions have higher pH values. Thus for the hexacyano-complexes, E is given by  

The simple titrations of iron (II) or (III) ions use redox titrations but because of their redox nature, potentiometric or other electrochemical methods may be as useful. 

When complexed with bipyridine or phenanthroline, strongly coloured complexes of Fe(II) or Fe(lII) are formed. These are the basis of spectrophotometric methods of their determination. 

Gravimetric analysis is usually carried out by precipitating Fe(III) in alkaline media and weighing the precipitate after heating to form iron (III) oxide. Precipitation is preceded by oxidation when the original solution is that of iron (II). 

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