Editing Concentration (section)

===Mole ratio===
{{main|Mixing ratio}}

The mole ratio <math>r_i</math> is defined as the amount of a constituent <math>n_i</math> divided by the total amount of all ''other'' constituents in a mixture:

:<math>r_i = \frac{n_i}{n_\mathrm{tot}-n_i}.</math>

If <math>n_i</math> is much smaller than <math>n_\mathrm{tot}</math>, the mole ratio is almost identical to the mole fraction.

The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole ratios.