Question

The weight of iron which will be converted into its oxide $\left( Fe _{3} O _{4}\right)$ by the action of $18\, g$ of steam on it will be (At. wt. of $Fe =56$ )

• A. 168 g
• B. 84 g
• C. 42 g
• D. 21 g

Answer 1

Answer: (C)

42 g

Answer 2

$\underset{3 \times 56\, g}{3 Fe} +\underset{4 \times 18\, g}{4 H _{2} O} \longrightarrow Fe _{3} O _{4}+4 H _{2}$ $4 \times 18\, g\, H _{2} O \equiv 3 \times 56\,g\, Fe$ $\therefore 18\, g\, H _{2} O \equiv \frac{3 \times 56}{4}$ $\equiv 42\, g$