Q.

The mass of iron converted into Fe3O4 by the action of 18 g of steam is:

(Given: Molar mass of H, O and Fe are 1, 16 and 56 g mol-1 respectively)

Assume iron is present in excess.                       [2026]

1 2.1 g  
2 4.2 g  
3 21 g  
4 42 g  

Ans.

(4)

Moles of steam=Given mass of H2OMolar mass of H2O

=18 g18 g mol-1=1 mol

3Fe(s)+4H2O(g)⟶Fe3O4(s)+4H2(g)

By stoichiometry:

nFe3=nH2O4⇒nFe3=14

nFe=34

Mass of Fe=Moles of Fe×Molar mass of Fe

                      =34×56 g=42 g