A mole is defined as quantity of a given substance that contains as many molecules or formula units as the number of atoms in exactly 12g of carbon-12.
The number of atoms in 12-g sample of carbon-12 is called Avogadro's number which is 6.02 x 1023.
Terms mole like a dozen refers to a perticular number of things.A dozen egg equals 12 eggs and a mole of ethanol equals 6.02 x 1023 molecules.
1 mole of H atoms = 6.02 x 1023 H atoms
1 mole O atoms = 6.02 x 1023 O atoms
1 mole H2 molecules = 6.02 x 1023 H2 molecules
1 mole H2O molecule = 6.02 x 1023 H2O molecules
In using terms moles for ionic substances we mean the number of formula units of substance.For example,
A mole of sodium carbonate,Na2CO3 is a quantity containing 6.02 x 1023 Na2CO3 units.But each formula units of Na2CO3 contains two Na+ ion and one CO32- ion.So, a mole of Na2CO3 also contains
2 x 6.02 x 1023 Na+ ion and 1 x 6.02 x 1023 CO32- ion
Mole and Molar mass
A mole represents not only a specific number of particles but also a definite mass of a substance as represented by its formula.