A sample of ferrous oxide has actual formula Fe0.93O1.00 . In this sample, what fraction of metal ions are Fe2+ ions? What type of non-stoichiometric defect is present in this sample?

 

 
Let the formula of the sample be (Fe2+)x.(Fe3+)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)
 
 x + 32y = 1              ...(iii)
 
On subtracting equation(i) from equation (iii) we have
32y - y = 1 - 0.93
                12y = 0.07                   
                  y = 0.14                     
 
 
On putting the value of y in equation (i), we get
x + 0.14 = 0.93
          x = 0.93 - 0.14            
           x = 0.79                   
 
Fraction of Fe2+ ions present in the sample = 0790.93 = 0.849
 
Metal deficiency defect is present in the sample because iron is less in-amount than that required for stoichiometric composition.