# What is a "mole"?

The mole is simply a number such as a $\text{dozen}$, or a $\text{Bakers' dozen}$, or a $\text{Botany Bay dozen}$...............
Of course, the mole is an exceedingly large number, i.e. $6.022 \ldots . . \times {10}^{23} \cdot m o {l}^{-} 1$. Why should we use it? Well if I have $6.022 \times {10}^{23}$ ""^1H atoms, I have a mass of $1.0 \cdot g$ precisely; or if I have $6.022 \times {10}^{23}$ ""^12C atoms, I have a mass of $12.0 \cdot g$ precisely. It is thus the link between the submicro world of atoms and molecules to the macro world of grams, and kilograms, and litres - that which we can weigh out on a balance, or can measure in a beaker. So can you tell me the MASS of $1 \cdot m o l$ of ""^12CH_4 molecules?