Question

Which of the following molecular formula and type of defect are correct for the following statement? ``In FeO crystal, some \(Fe^{2+}\) ions are missing and the loss of positive charge is made up by the presence of \(Fe^{3+}\) ions.''

• A. \(Fe_{0.95}O\) and metal excess defect
• B. \(Fe_{1.05}O\) and metal deficiency defect
• C. \(Fe_{0.95}O\) and metal deficiency defect
• D. \(Fe_{1.05}O\) and metal excess defect

Hint:

Metal deficiency defects are common in transition metal compounds. They arise when some metal ions are missing and charge balance is maintained by the presence of metal ions in higher oxidation states.

Answer 1

The Correct Option is C

Step 1: Understand the defect present in FeO.
In the crystal of iron(II) oxide, some \[ Fe^{2+} \] ions are absent from their normal lattice positions.
This creates cation vacancies in the crystal lattice.
Therefore, the number of metal ions becomes less than the number expected from the ideal stoichiometric formula.

Step 2: Compensation of charge.
The loss of positive charge due to missing \[ Fe^{2+} \] ions is compensated by the oxidation of some remaining \[ Fe^{2+} \] ions into \[ Fe^{3+} \] Thus, electrical neutrality of the crystal is maintained.

Step 3: Identify the type of defect.
Since metal cations are missing from their lattice sites, the crystal possesses a metal deficiency defect This type of defect is commonly observed in transition metal oxides such as FeO, NiO, and CoO.

Step 4: Determine the formula.
Because some iron ions are absent, the actual number of iron atoms becomes less than the number of oxygen atoms expected in the ideal formula FeO.
Hence, the composition becomes approximately \[ Fe_{0.95}O \] which indicates fewer iron atoms than required by the stoichiometric ratio.

Step 5: Final conclusion.
Therefore, the correct molecular formula and defect are \[ \boxed{Fe_{0.95}O\ \text{and metal deficiency defect}} \] Hence, the correct option is \[ \boxed{(3)} \]