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Answer:

From the chemical formula of a compound you can learn about its composition:

  • kind of atoms (elements) that form it, and
  • the ratios (relative proportions of number of atoms)

Also, with the ratios and the atomic masses of each kind of atom, you can obtain the mass composition (%) of the compound.

Explanation:

Using indexes (subscripts), the chemical formula of a compound shows  the elements (kind of atoms) in the compound and the relative proportions of those elements.

The following example will show you how you learn that information from the chemical formula.

A very familiar compound is water and its chemical formula (also very familiar) is H₂O.

From that, you learn that water (a chemical compound):

  • Is formed of hydrogen and oxygen atoms

  • Has two atoms of hydrogen per each atom of oxygen (2:1 ratio)

  • Molar mass: Using the atomic masses of hydrogen and oxygen obtain the mass of one mole of water molecules:

        * hydrogen, H: 2 × 1.008 g/ mol = 2.016 g/,ol

        * oxygen, O: 1 × 15.999 g/mol = 15.999 g/mol

        * Molar mass of water: 2.016 g/mol + 15.999 g/mol = 18.015 g/ mol

  • Percent composition:

        * H: (2.016 g/mol / 18.015 g/mol) × 100 = 11.19%

        * O: (15.999 g/mol / 18.015 g/mol) × 100 = 88.81%

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