why we can't get pure distillations with a hexane-octane mix? why simple distillation don't work in this case?

Question

hexane boiling point is 69 degrees celsius and octane is 126 degrees. Their boiling points are not too close together. do you see what I mean?

Answer 1

The boioling points are too close together for a clean separation. You have to distil with a fractionating column, in which the condensing liquid descending mixes intimatekly with the vapor going up, giving the effect of 10 or 1000 sequential simple distillations (called plates).