Question

i) When is simple distillation method of separating mixtures used? Write the steps to separate a mixture of acetone
and water by simple distillation.
ii) Oxygen,argon and nitrogen boils at -183 ℃, -185.8 ℃ and
-195.8 ℃ respectively. Answer the following questions:
(a) Arrange the gasses in the increasing value of boiling
point.
(b) Which gas liquifies first on cooling?
(c) Which gas is separated first when the liquid air is
warmed up?

[8 Marks]

Answer 1

i) Simple distillation is used to separate the mixture of two miscible liquids where difference between their boiling points is greater than 25 ºC.

Acetone and water are miscible liquids with a boiling point difference more than 25 ºC. So, they can be separated by the method of simple distillation.
[2 Marks]

Steps involved in simple distillation:

1. Take the mixture in a distillation flask and attach a thermometer to it. [0.5 Mark]
2. Assemble the apparatus as shown in the figure. [0.5 Mark]
3. Heat the mixture slowly while keeping an eye on the thermometer. [0.5 Mark]
4. Since acetone has lower boiling point, it vaporises first and condenses in the condenser, which is finally collected in the beaker. [0.5 Mark]

Diagram: Simple distillation
[1 Mark]
ii)
(a) Nitrogen < Argon < Oxygen
[1 Mark]
(b) Oxygen
[1 Mark]
(c) Nitrogen
[1 Mark]