Stoichiometry
1.0 The Mole
1.0 The Mole
The term ‘mole’ is a Latin word which means heap or pile. A mole of atom is a collection of atoms whose total weight is equal to the gram atomic weight.
As equal number of moles of different elements contain equal number of atoms, it is very easy to express the amount of a substance in terms of moles. Just as a dozen means twelve objects, in the similar fashion, a mole is a collection of a ‘definite number’ of particles, viz., atoms, molecules, ions or electrons.
This ‘definite number’ is called Avogadro number which is equal to $6.023 \times {10^{23}}.$
Thus, a mole can be defined as, “the amount of a substance containing as many atoms, molecules, ions, electrons or other elementary entities as there are carbon atoms in exactly $12g$ of $C-12”.$
Now-a-days, gram-molecules and gram-atom are termed as a mole of molecules and a mole of atoms respectively, e.g., $1$ gram-molecule of chlorine and $1$ gram atom of chlorine are expressed as $1$ mole of $Cl_2$ and $1$ mole of $Cl$ respectively.
The number of moles can be calculated by a number of formulae depending upon the data given:
No. of moles of molecules is calculated using $$\frac{{Wt.{\text{ of substance in g}}}}{{Mol.{\text{ wt}}{\text{. of substance}}}}$$
No. of moles of atoms is calculated using $$\frac{{Wt.{\text{ of element in g}}}}{{At.{\text{ wt}}{\text{. of the element}}}}$$
No. of moles of gas is calculated using $$\frac{{Volum{\text{e of the gas at STP}}}}{{Sta{\text{ndard molar volume (i}}{\text{.e}}{\text{. 22}}{\text{.4L)}}}}$$
