Determine the formula of a chemical compound if the mass fractions (%) of its constituent elements

Determine the formula of a chemical compound if the mass fractions (%) of its constituent elements are equal: P -43.66% and O – 56.34%

Solution:

1. Let’s designate: x – molecular weight of a substance, a – number of phosphorus atoms, b – number of oxygen atoms.

2. The relative atomic mass of phosphorus is 31, oxygen is 16.

3. Let’s compose the following expressions:

0.4366 = 31a / x;

0.5634 = 16b / x;

4. Let us express the molecular weight of a substance:

x = 31a / 0.4366 = 71a;

x = 16b / 0.5634 = 28.4b;

5. Equate expressions: 71a = 28.4b. The obtained values are: a = 2, b = 5. The unknown substance is phosphorus oxide, its formula is P2O5.

Answer: The formula of the chemical compound is P2O5.