Question

A compound has a molar mass of 92.02 grams/mole, and its percent composition is 30.4% nitrogen (N) and 69.6% oxygen (O). What is its molecular formula? A. N2O4 B. NO2 C. N2O D. N4O2

Answer 1

The answer is: A. N2O4.

M(NₓOₙ) = 92.02 g/mol; molar mass of unknown compound.

If we take 100 grams of sample:

m(N) = 0.304 · 100 g.

m(N) = 30.4 g; mass of nitrogen.

n(N) = 30.4 g ÷ 14.01 g/mol.

n(N) = 2.17 mol; amount of nitrogen.

m(O) = 0.696 · 100 g.

m(O) = 69.6 g; mass of oxygen

n(O) = 69.6 g ÷ 16 g/mol.

n(O) = 4.35 mol; amount of oxygen.

n(N) : n(O) = 2.17 mol : 4.35 mol.

n(N) : n(O) = 1 : 2.

Answer is N₂O₄ or NO₂, so we must find molar mass.

M(N₂O₄) = 2Ar(N) + 4Ar(O) · g/mol.

M(N₂O₄) = 92.02 g/mol.