Question
Analysis shows that FeO has a non-stoichiometric composition with formula Fe0.95O. Give reason.
Solution
The non-stoichiometry reflect the ease of oxidation of Fe2+ to Fe3+ effectively replacing a small portion of Fe2+ with two thirds their number of Fe3+. Thus for every three 'missing' Fe2+ ions, the crystal contains two Fe3+ ions to balance the charge. i.e. 3Fe2+ = 2Fe3+ to maintain electrical neutrality.
