Mole fraction refers to the fraction of a component of a solution when the amounts (component and solution) are expressed in moles. In other words, the Mole fraction of a component is the ratio of moles of that particular component to the total moles of the solution.
Mole fraction (𝒳i) can be calculated by
ni = Mole of ith component of the solution
ntot = Mole of the solution
Suppose a solution contains 3 components (two solutes, A and B, and a solvent C)
nA = Mole of component A
nB = Mole of component B
nC = Mole of component C
Since the solution contains only three components, two solutes, and a solvent, the total moles (ntot) of the solution will be equal to
ntot = nA + nB + nC
Therefore above equation can also be written
Properties of Mole Fraction:
1. Mole fraction is dimensionless:
Since the value of mole fraction is obtained by dividing the mass of a component by the total mass of solution, it is dimensionless. However, sometimes it is written as mole/mole.
The sum of all Mole fractions is equal to 1.
In above example
𝒳A + 𝒳B + 𝒳C = 1
2. Mole fraction is independent of temperature
In contrast to density, the Mole fraction is independent of temperature i.e., if temperature changes, the value of the Mole fraction does not change.