20. Determine the molecular
formula of an oxide of iron in
which the mass percent of iron
and oxygen are 69.9 and 30.1
respectively given that molar
mass of the oxide is 159.69 g
Imol?
Answers
Answer:
The iron oxide has 69.9% iron and 30.1% dioxygen by mass.
Thus, 100 g of iron oxide contains 69.9 g iron and 30.1 g dioxygen.
The number of moles of iron present in 100 g of iron oxide are
55.8
69.9
=1.25.
The number of moles of dioxygen present in 100 g of iron oxide are
32
30.1
=0.94.
The ratio of the number of oxygen atoms to the number of carbon atoms present in one formula unit of iron oxide is
1.25
2×0.94
=1.5:1=3:2.
Hence, the formula of the iron oxide is Fe
2
O
3
.
ANSWER-
The iron oxide has 69.9% iron and 30.1% dioxygen by mass.
Thus, 100 g of iron oxide contains 69.9 g iron and 30.1 g dioxygen.
The number of moles of iron present in 100 g of iron oxide are 55.8/69.9 =1.25.
The number of moles of dioxygen present in 100 g of iron oxide are
32/30.1 =0.94.
The ratio of the number of oxygen atoms to the number of carbon atoms present in one formula unit of iron oxide is
1.25/2×0.94. =1.5:1. =3:2.
Hence, the formula of the iron oxide is Fe2O3 .