Mole ConceptMedium
Question
The mass of iron converted into ${Fe}_{3}O_{4}$ by the action of 18 g of steam is :
(Given : Molar mass of H, O and Fe are 1, 16 and $56\text{ }g{\text{ }mol}^{- 1}$ respectively)
Assume iron is present in excess :
Options
A.2.1 g
B.4.2 g
C.21 g
D.42 g
Solution
Sol. [Key Concept: Balance $3Fe + 4H_{2}O \rightarrow \ {Fe}_{3}O_{4} + 4H_{2}$; from the moles of steam find the Fe converted.]
$${3Fe(s) + 4H_{2}O(g) \rightarrow {Fe}_{3}O_{4}(\text{ }s) + 4H_{2}(\text{ }g) }{n_{\text{steam}\text{~}} = \frac{18}{18} = 1 }$$$n_{Fe}$ required $= \frac{3}{4}$
$$\begin{matrix} & \text{~}\text{mass of Fe required}\text{~} = \frac{3}{4} \times 56 \\ & \ = 42gm \end{matrix}$$
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