Question

The composition of a sample of wustite is $F{e}_{0.93}O$. What percentage of the iron is present in the form of Fe (III)?

• A. $5\%$
• B. $7.08\%$
• C. $15.05\%$
• D. $23.6\%$

Answer 1

Answer: (C)

In pure iron oxide $(FeO)$, iron and oxygen are present in the ratio $1:1$.
However, here number of $F{e}^{2+}$ present $=0.93$
Or No. of $F{e}^{2+}$ ions missing $=0.07$
Since each $F{e}^{2+}$ ion has $2$ positive charge,
the total number of charge due to missing $(0.07)F{e}^{2+}$ ions $=0.07\times 2=0.14$
To maintain electrical neutrality, $0.14$ positive charge is compensated by the presence of $F{e}^{3+}$ ions.
Now since, replacement of one $F{e}^{2+}$ ion by one $F{e}^{3+}$ ion increases one positive charge, $0.14$ positive charge must be compensated by the presence of $0.14F{e}^{3+}$ ions.
In short, $0.93F{e}^{2+}$ ions have $0.14F{e}^{3+}$ ions
$100F{e}^{2+}$ ions have $=\frac{0.14}{0.93}\times 100=15.05\%$