Question

What is the meaning of the chemical formula of a compound? What information do we get from the formula? Write your answer by giving a suitable example.

Answer 1

The chemical or molecular formula of a substance represents the actual number of atoms of elements present in one molecule of that substance, in terms of symbols, e.g. formula of sodium chloride is NaCl, acetic acid is C₂H₄O₂

A formula gives the following information:

(a) Formula represents 1 mole of the substance.

For example, NaCl represents one mole or 02 x 10²³ molecules of sodium chloride.

(b) The formula gives the name of all the elements present in the molecule.

For example, elements in Na₂SO₄ are sodium (Na), sulphur (S), and oxygen (O).

(c) The formula gives information about the number of atoms of elements present in one molecule

e.g. Na₂SO₄ tells that there are two-mole atoms of sodium (Na), a onemole atom of sulphur (S) and four-mole atoms of oxygen (O) in the molecule.

(d) Molecular formula represents one gram molecular weight or molar mass of the substance. Atomic masses of sodium, sulphur and oxygen are 23, 32 and 16 respectively, so the molecular weight or molar mass of sodium sulphate (Na2SO4) is- 

(23 x 2) + 32 + (16 x 4)

= 46 + 32 + 64 = 142

Also, the elements sodium, sulphur, and oxygen are present in the compound in the simplest ratio 

23: 16: 8 parts by weight.