Mole/Examples/Water

Example of Mole
$1$ mole of water has a mass of (approximately) $18$ grams.

Proof
By definition, a molecule of water is composed of:
 * $2$ atoms of hydrogen
 * $1$ atom of oxygen.

It follows that $1$ mole of water is composed of:
 * $2$ moles of hydrogen
 * $1$ mole of oxygen.

The (by far) most plentiful isotopes of these elements are:


 * hydrogen-$1$, with an atomic mass of approximately $1$
 * oxygen-$16$, with an atomic mass of approximately $16$.

From Mass of Mole of Isotope of Element:
 * the mass of $1$ mole of hydrogen-$1$ is $1 \ \mathrm g$
 * the mass of $1$ mole of oxygen-$16$ is $16 \ \mathrm g$.

Hence the mass of $1$ mole of water is $2 \times 1 + 16 = 18$.