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. Molar mass of this oxide is

170.0 g mol−1

.​

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

.