Methods of Separating Mixtures (VI)

SUBLIMATION

This is a separation method involving solids. The solids involved should be a solid that sublimes and the other should be a solid that does not sublime. Some solids, when heated change directly from solid to gas without passing through liquid. The normal procedure should be:

Solid → Liquid → Gas

But with sublimation, the solid changes directly to gas without passing through the liquid state. This method deals with the heating of the two solids. The solid which sublimes will change into gas thus vapour. The vapour is then collected. The other solid which does not sublime still remains in the container. Let’s perform an experiment on this to broaden our understanding.

Activity : Sublimation

Material : Sodium chloride, ammonium chloride, water, blue litmus paper, evaporating basin, ice cold water, Ice cubes, Bunsen burner, scrapper, powdered common salt, beakers.

Method:

Dissolve a little sodium chloride and a little ammonium chloride in small amounts of water into different beakers.

Dip blue litmus paper in each of the solutions.
a. Record what you observe.

Mix about 10g of powdered common salt with about 10g of ammonium chloride in a beaker thoroughly.

Put the beaker on a tripod and cover the mouth of the beaker with an evaporating basin.

Pour a little ice-cold water with a few ice cubes into the evaporating dish.

The content in the beaker is heated using a Bunsen burner. The content should be heated until some solid are collected on the bottom of the evaporating dish.

Scrape this into a clean beaker.

A little amount of water is added to the scrapped solid and stir well to dissolve.

Put blue litmus paper in the solution.
b. Did the blue litmus paper change colour?
c. What was the colour of the litmus paper?
d. What conclusion can you draw about the substance scrapped off?
e. Why were the ice cubes used?

Diagram