Mole fraction

Mole fraction

Mole fraction refers to the fraction of a component in a solution when the amounts (component and solution) are expressed in moles. In other words, 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)

Mole fraction of component A (𝒳A) =
Mole fraction of component B (𝒳B) =
Mole fraction of component C (𝒳C) =
Where
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

Mole fraction of component A (𝒳A)
Mole fraction of component B (𝒳B)
Mole fraction of component C (𝒳C)
Mole fraction is dimensionless:

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

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

𝒳A + 𝒳B + 𝒳C = 1

Independent of temperature

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