Example 2 - Molecular Formula

What is the mass of metal X that can combine with 14.4g of oxygen to form X oxide with molecular formula X2O3. (RAM: O = 16; X = 56 )

Answer:
Number of mole of oxygen = 14.4 16 =0.9 mol From the molecular formula, we learn that  the ratio of element X to oxygen X:= 2:3 Therefore, the number of mole of X =0.9× 2 3 =0.6 mol Number of mole, n =  mass Molar mass 0.6= mass 56* mass=33.6g The mass of element X = 33.6g *Molar mass of a substance = Relative atomic mass of the substance