Question

A sample of ferrous oxide has actual formula $F{e}_{0.93}{O}_{1.00}$ In this sample, what fraction of metal ions are $F{e}^{2+}$ ions ? What type of non-stoichiometry defect is present in this sample?

Answer 1

Let the formula of the sample be $(F{e}^{2+}{)}_x$ $(F{e}^{3+}{)}_y$ O

On looking at the given formula of the compound

x+y=0.93 ........(i)

Total positive charge on ferrous and ferric ions should balance the two units of negative charge on oxygen

Therefore, 2x+3y=2 ..............(ii)

$\Rightarrow$ $x+\frac{3}{2}y=1$ .............(iii)

On subtracting equation (i) from equation (iii) we have

$\frac{3}{2}y-y=1-0.93$

$\Rightarrow$ $\frac{1}{2}y=0.07$

$\Rightarrow$ y=0.14

On putting the value of y in equation (i), we get

x+0.14=0.93

$\Rightarrow$ x=0.93-0.14

$\Rightarrow$ x=0.79

Fraction of $F{e}^{2+}$ ions present in the sample $=\frac{0.79}{0.93}=0.849$

Metal deficiency defect is present in the sample because iron is less in amount than that required for stoichiometric composition.