Question

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 the molar mass of oxide is 159.8gmol-1

.

(Atomic mass of iron & oxygen are 55.85u & 16u respectively)​

Answer 1

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

.