Question

18 g of steam reacted with iron to form $Fe_3O_4$, how much iron will be consumed.

• A. 21 gm
• B. 42 gm
• C. 84 gm
• D. 10.5 gm

Answer 1

The Correct Option is B

Mole-to-mole and mole-to-mass conversion based on a balanced chemical equation.

LOGIC:
1. Reaction: $3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2$
2. Given mass of steam = 18 g. Since molar mass of water is 18 g/mol, we have exactly 1.0 mole of steam.
3. Stoichiometric relationship: 4 parts water reacts with 3 parts iron.
4. Ratio: $\frac{\text{Moles of } Fe}{\text{Moles of } H_2O} = \frac{3}{4}$
5. Moles of $Fe = \frac{3}{4} \times 1 = 0.75 \text{ moles}$.
6. Mass of $Fe = \text{moles} \times \text{atomic weight} = 0.75 \times 56 = 42 \text{ g}$.

Final result is 42 gm.