Chemistry, Third edition

SEPARATING SOLIDS

Separating solids

If a solid sublimes(passes from the solid state directly to the vapour state), this fact

can be used to separate the solid from a mixture in which there are other solids. The

mixture is heated and the sublimed material condensed on a cool surface.

A simple form of the apparatus, used to separate a mixture of salt and iodine, is

shown in Fig. 19.10.

Often the process is carried out under reduced pressure, so that the substance can

be sublimed at a lower temperature (Fig. 19.11).

19.3

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Fig. 19.10Separation by sublimation. Fig. 19.11Sublimation under reduced pressure.

Separations

(i) Water and ethoxyethane (diethylether) are immiscible liquids. What apparatus

would you use to separate them?

(ii)A mixture of sugar and sand needs to be separated. What techniques would

you use?

(iii)The solubilities of potassium chloride and potassium chlorate in water are as

follows:

Substance Solubility in water/grams per 100 cm^3 water

at 20 °C at 100 °C

Potassium chloride 35 57

Potassium chlorate 8 54

Given a mixture of 8 g potassium chloride and 25 g of potassium chlorate, how

would you obtain a pure sample of potassium chlorate?

(iv)How would you separate two miscible liquids, with boiling points of 80 °C and

60 °C, respectively?

(v)What technique would you use to obtain pure water from seawater?

Exercise 19B