Editing Concentration (section)

===Mass fraction===
{{main|Mass fraction (chemistry)}}

The mass fraction <math>w_i</math> is the fraction of one substance with mass <math>m_i</math> to the mass of the total mixture <math>m_\mathrm{tot}</math>, defined as:

:<math>w_i = \frac {m_i}{m_\mathrm{tot}}.</math>

The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions.