134.

Define Avogadro’s law. Taking a suitable example, prove that it is not in contradiction with Dalton’s atomic theory.

Avogadro’s law states that ‘equal volumes of all gases under similiar conditions of temperature and pressure contain equal number of molecules.’
On applying Avogadro’s law to the reaction between hydrogen and oxygen to form water vapours, we have,

Hydrogen    +   Oxygen          Water vapours
2 volumes         1 volume              2 volumes(experimental)
2n molecules     n molecules          2n molecules
                                      (Avogadro's hypothesis)

2 moleucles    +  1 molecule        2 molecules
1 molecule     +   1/2 molecule     1 molecule

This means that one molecule of water is made of 1 molecule of hydrogen and 1/2 molecule of oxygen (i.e. one atom of oxygen). Since the molecules can be subdivided, the result is not in conflict with Dalton’s atomic theory.