Question

Equivalent weight of iron in $F{{e}_{2}}{{O}_{3}}$ would be:
(Fe=56)
(A) 28
(B) 56
(C) 18.6
(D) 112

Answer 1

Hint: Start by calculating the oxidation state of iron in $F{{e}_{2}}{{O}_{3}}$. We know that, equivalent weight is molecular weight divided by number of reacting species. Accordingly, substitute the values and find out the answer.

Complete answer:
- In this question, we need to find the equivalent weight of iron in $F{{e}_{2}}{{O}_{3}}$.
- First, we need to start by finding the oxidation state of iron then only we will get the number of reacting species.
- Let’s assume the oxidation state of iron, Fe as ‘x’.
- In $F{{e}_{2}}{{O}_{3}}$, there are two Fe atoms so oxidation state will be ‘2x’ and three oxygen atoms having oxidation state, -2.
- Therefore, we get,
\[2x+\left( 3\times -2 \right)=0\]
\[\begin{align}
  & 2x=+6 \\
 & \therefore x=+3 \\
\end{align}\]
- So, we know iron is present in +3 oxidation state. Therefore, the compound, $F{{e}_{2}}{{O}_{3}}$ is ferric oxide.
- Now, we know that the number of reacting species in iron is 2.
- We have the formula, $\text{Equivalent weight=}\dfrac{\text{Molecular weight}}{\text{Number of reacting species}}$
- Molar mass of Fe is given as 59.
- Therefore, Equivalent weight $=\dfrac{59}{3}=27.923\approx 28$
- Hence, the equivalent weight of iron in ferric oxide, $F{{e}_{2}}{{O}_{3}}$ is 28g/mol.

Therefore, the correct answer is (A) 28.

Note: Remember to calculate the equivalent weight of any compound just divide the molecular weight by number of reacting species. To find the equivalent weight of one element present in the compound, find the oxidation state of that element and that oxidation state will be the number of reacting species.