# What is the mol fraction of water?

Feb 6, 2017

Well, what's the definition of mol fraction?

${\chi}_{i} = {n}_{i} / \left({n}_{1} + {n}_{2} + . . . + {n}_{N}\right)$

where ${\chi}_{i}$ is the mol fraction of component $i$, ${n}_{i}$ is the mols of $i$, and the denominator contains the sum of the mols of everything in the solution.

With just water by itself, we have:

${\chi}_{i} = {n}_{{H}_{2} O} / \left({n}_{{H}_{2} O}\right) = 1$

since ${n}_{\text{tot}} = {n}_{{H}_{2} O}$ in a pure-water "solution".