A sample of ferrous oxide has actual formula `Fe_(0.93)O_(1..00)`. In this sample what fraction of metal ions are `Fe^(2+)` ions? What type of non-stoichiometric defect is present in this sample ?

Options

A. (i)-0.849 , (ii)-Metal deficiency
B. (i)-0.790 , (ii)-Metal deficiency
C. (i)-0.145, (ii)-Metal excess
D. (i)-0.93 , (ii)-Vacancy defect

Answer

A

Explanation

Let the formula of sample be `(Fe^(2+))_x (Fe^(3+))_yO`
From the formula of the compound , x+y =0.93 …(i)
Total positive charge on `Fe^(2+)` and `Fe^(3+)` should balance the two units of negative charge on oxygen . Hence 2x+3y=2
`rArr x + 3/2 y=1`...(ii)
On subtracting equation (i) from (ii)
`3/2y-y=1-0.93 rArr 1/2y=0.07`
`rArr` y=0.14
On putting the value of y in equation (i), x+0.14 = 0.93 `rArr` x=0.93-0.14
or x=0.79
Fraction of `Fe^(2+)` ions present in the sample `=0.79/0.93`=0.849
Metal deficiency defect is present in the sample because iron is less in amount than that required for stoichirometric composition.