Question

Why are concentration units of mole fraction used in some colligative properties calculations?

Answer 1

something like this \[{\frac{ \text{moles }a} {\text{moles } ab} }\]

Answer 2

mole fraction is used most often because colligative properties depends mainly on the quantity of solute molecules present, not necessarily their identity. The stronger (more solut molecules) a solution is, the greater teh mole fraction, and the greater the coligative property difference.