Question

Please explain why the fractional distillation of two components is easily accomplished if the components have boiling points that differ 20Celsus or more . Please also draw a phase diagram.

Answer 1

Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one of fraction of the compound will vaporize.

Lets say we have two liquids A and B with boiling points 60 and 80 degrees respectively. Now with both liquids rising to the column, the liquid with a lesser boiling point will be able to cross the column when the temperature of the column reaches 60 degree mark whereas the liquid with higher boiling point would still loose its energy to the column to further increase its temperature and condensing back to become a liquid.

If the two liquids will have a large difference in boiling point, it will be easier to separate them by distillation.Because boiling point and heat of vaporization are correlated quantities: A liquid with a large heat of vaporization must have strong inter-molecular interactions/attraction. This will result in a high boiling point.The vapors of liquid with high b.p have stronger intermolecular force of attraction between the molecules than those liquid vapour with lower b.p. Every liquid requires certain amount of heat energy to get converted into vapor form. In case of liquids with high b.p, more heat energy is required. In fractional distillation as you would know contains different columns. A liquid with high b.p, due to its high tendency to bind together with other molecules (strong cohesive forces), as soon as it loses energy, the degree of randomness (distance spread apart from each other) decreases and hence they condense faster in the fractionating column.