question_answer 111)

  Why is it not possible to obtain pure ethanol by fractional distillation? What general name is given to binary mixtures which show deviation from Raoult's law and whose components cannot be separated by fractional distillation. How many types of such mixtures are there?

Answer:

                  The solution or mixture having same composition in liquid as well as in vapour phase and boils at a constant temperature is known as azeotropes. Due to constant composition it Can?t be separated by fractional distillation. There are two types of azeotropes (i) Minimum boiling azeotropes Solutions which show large positive deviation from Raoult's law form minimum boiling azeotropes at a specific composition, e.g., ethanol ?water mixture (ii) Maximum boiling azeotropes Solutions which show large negative deviation from Raoult's law form maximum boiling azeotropes. e.g., solution having composition 68% HNO3 and 32% water by mass.