Mass fraction

Mass fraction

Mass fraction refers to the fraction of a component in a solution when the amounts (component and solution) are expressed in mass (weight). In other words, mass fraction is the ratio of the mass (or weight) of a component to the total mass (or weight) of the solution.

Mass fraction (ωi) can be calculated by
Where
mi = Mass of ith component of the solution

mtot = Mass of the solution

Suppose a solution is prepared by dissolving two solutes A and B in a solvent C.

Mass fraction of component A (ωA)
Mass fraction of component B (ωB)
Mass fraction of component C (ωC)
Where
mA = Mass of component A
mB = Mass of component B

mC = Mass of component C

Since the solution contains only three components, two solutes and a solvent, the total mass of the solution (mtot) will be equal to

                                                                     mtot =  mA + mB + mC

Therefore above equation can also be written
Mass fraction of component A (ωA)
Mass fraction of component B (ωB)
Mass fraction of component C (ωC)
Mass fraction is dimensionless:

Since value of mass fraction is obtained by dividing mass of a component by total mass of the solution, it dimensionless. However, sometimes it is written as gram/gram or Kg/Kg.

The sum of all mass fraction is equal to 1.
In above example

ωA + ωB + ωC = 1

Independent of temperature

In contrast to density, mass fraction is independent of temperature i.e., if temperature changes, the value of mass fraction does not change.