Calculate the mass fractions of elements in the nitric acid HNO3.

To calculate the mass fraction of elements in the composition of a substance, it is necessary to calculate the molar mass of nitric acid by adding the atomic masses of each element:
Mr (HNO3) = 2 + 14 + 16 • 3 = 63 g / mol.
Let us determine the mass fractions of hydrogen, nitrogen and oxygen in the acid:
W (H) = n • Ar (H) / Mr (HNO3) = 1/63 = 0.016 (1.6%).
W (N) = n • Ar (N) / Mr (HNO3) = 14/63 = 0.222 (22.2%).
W (O) = n • Ar (O) / Mr (HNO3) = 3 • 16/63 = 0.762 (76.2%).