Solved: CHEMISTRY Question for NEET

NEET CHEMISTRYMedium

What fraction of Fe exists as Fe(III) in $Fe_{0.96}O$ ? (Consider $Fe_{0.96}$ to be made up of Fe(II) and Fe(III) only)

1/12

0.08

1/16

1/20

Establish Charge Neutrality: The compound $Fe_{0.96}O$ is neutral. The oxide ion ( $O^{2-}$ ) has a charge of $-2$ . Therefore, the total positive charge contributed by $0.96$ moles of Iron atoms must be $+2$ .
Set up Equations:

Let the fraction of $Fe^{3+}$ be $x$ and the fraction of $Fe^{2+}$ be $(1-x)$ .
Alternatively, consider 100 formula units of $Fe_{0.96}O$ contains 96 Fe atoms and 100 O atoms.
Total charge of Fe atoms = Total charge of O atoms = $200$ .
Let number of $Fe^{3+}$ be $a$ and $Fe^{2+}$ be $b$ .
Eq 1 (Atom balance): $a + b = 96$
Eq 2 (Charge balance): $3a + 2b = 200$

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