# What is meant by the term 'mole' (and its unit, 'mol') in chemistry? (Hint: not a small burrowing mammal)

Apr 26, 2016

A $\text{mol}$ is essentially a large quantity, equal to about $6.022 \times {10}^{23}$ (Avogadro's number).

The number is chosen, though, so that a large quantity of quantum-sized objects (i.e. atoms, molecules, etc) can be described in more manageable, less awkward values.

For instance, instead of saying we have $6.022 \times {10}^{23}$ atoms, which is a bit awkward, it is more convenient to say:

6.022xx10^23 cancel"atoms" xx ("1 mol")/(6.022xx10^23 cancel"atoms")

$=$ $\textcolor{b l u e}{\text{1 mol of atoms}}$

It's just a new unit to express a large quantity of things.

$\text{1 mol}$ of pictures is the same quantity as $\text{1 mol}$ of thumbdrives is the same quantity as $\text{1 mol}$ of paper towels. They aren't the same mass, but there are the same number of them.

We have defined our units so that, for example, the atomic mass of $\text{_6^12"C}$, the carbon-12 isotope, is $\text{12 amu}$ (atomic mass units). That is the mass of one atom of carbon-12. But if we express the mass as $\text{12 g}$ instead, that is the mass of $\text{1 mol}$ of carbon-12 atoms.

The $\text{mol}$ concept is handy because $\text{1.0079 g}$ of $\text{H}$ is $\text{1 mol}$ and $\text{15.999 g}$ of $\text{O}$ is $\text{1 mol}$, etc.

Suppose we have $\text{25 g}$ of ${\text{N}}_{2}$ and want to know how many $\text{mol}$s that is.

The molar mass of $\text{N}$ atom is $\text{14.007 g/mol}$, so the molar mass of ${\text{N}}_{2}$ is $\text{28.014 g/mol}$.

25 cancel("g N"_2) xx ("1 mol N"_2)/(28.014 cancel("g N"_2))

$\approx \text{0.892 mol} ,$

which is a smaller number and easier to work with.