The compound containing nitrogen and oxygen has a molar mass of 756 g/mole. A certain amount of the compound has 4.2 g of nitrogen and 12 g of oxygen. As the molar mass of oxygen (O) is 16 g/mole, this is equivalent to 12/16 = 3/4 moles of oxygen and as the molar mass of nitrogen (N) is 14 g/mole, this is equivalent to 4.2/14 = 0.3 moles of nitrogen. Multiplying each by (20/3) gives 2 moles of nitrogen for every 5 moles of oxygen.
The empirical formula of the compound is N2O5. As the molar mass of the compound is 756, the molecular formula of the chemical compound is N14O35
The molecular formula of the compound is N14O35