Finding the molecular formula through molar mass and percenteges

Question

Compound has a molar mass of 283.89 g.mol^-1 and the following composition:

Phosphorus: 43.64%

Oxygen: 56.36%

Write the molecular formula of X.

Answer 1

Assume that you have 100 grams of the substance:

Phosphorus: 43.64%

43.64 g P x 1 mole P/30.97 g P = 1.41 mol P

Oxygen: 56.36%

56.36 g O x 1 mol O/16.00 g O = 3.52 mol O

Divide by least molar amount:

1.41/1.41 = 1 mol P

3.52/1.41 = 2.5 mol O

Multiply to derive whole numbers:

2 mol P

5 mol O

Empirical formula:

P2O5

Check molar mass: 283.89 g/mol