Calculate the mass fractions of an element in a substance in fractions of a unit of copper nitrate (11).

1. Find the molar mass of the substance CuNO3 (copper nitrate) – i.e. the mass of 1 mol of this substance. According to the periodic system, we find the atomic masses: copper – 64, nitrogen – 14, oxygen – 16 (remember that oxygen atoms in a substance – 3):

64 + 14 + 16×3 = 126 g / mol.

2. The mass fraction of which specific of the elements that make up the substance needs to be found – not specified, but all are found according to the same principle – proportions:

copper in 1 mol of substance – 64 g, share – 64: 126 = 0.51 (rounded value);

nitrogen in 1 mol – 14 g, proportion – 14: 126 = 0.11 (rounded value);

oxygen in 1 mol – 16×3 = 48 g, share – 48: 126 = 0.38.