He 64.8-g sample of the compound X2O5 contains 48.0 g of oxygen atoms. What is the molar mass of element X?

We calculate the molar mass of element X as follows:

No. of moles = 48/16 = 3.2 mol

Mass of X2 = 64.8 - 48 = 16.8 g

2 molesX/5 mole O = x / 3.00 moles O

x = 1.2 moles of X

Molar mass = 16.8g / 1.2 mol = 14 g/mol