The chemical formula for dinitrogen pentoxide is N₂O₅. The formula indicates that in one mole of N₂O₅, there are five moles of oxygen atoms.
Calculate the moles of N₂O₅ in 54 g.
n = m/M; where n = moles, m = mass (g), and M = molar mass (g/mol).
m(N₂O₅) = 54 g N₂O₅
M(N₂O₅) = (2×14 g/mol N) + (5×16 g/mol O) = 108 g N₂O₅/mol N₂O₅
n(N₂O₅) = 54 g N₂O₅/108 g N₂O₅/mol N₂O₅ = 0.50 mol N₂O₅
Calculate the moles of O in 0.50 mol N₂O₅.
0.50 mol N₂O₅ × 5 mol O/1 mol N₂O₅ = 2.5 mol O
Calculate the mass of 2.5 mol O.
m = n × M
n(O) = 2.5 mol O
M(O) = 16 g O/mol O
m(O) = 2.5 mol O × 16 g O/mol O = 40. g O to two significant figures
There are 40. g of oxygen in 54 g of dinitrogen pentoxide.