SS1 Second Term Chemistry Lesson Note – Standard Separation Techniques for Mixtures III

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WEEK 8

TOPIC: STANDARD SEPARATION TECHNIQUES FOR MIXTURES.

CONTENTS:

• Floatation
• Frostation (froth flotation)
• Pure and impure substances
• Test for purity

PERIOD 1: FLOATATION:

Floatation method is based on the wide difference in the densities of the components of the mixture. The method is used for the separation of a mixture of two solids in which one component is light and the other is heavy. On the addition of a liquid in which neither is soluble, one component sinks, while the other floats. e.g. a mixture of coarse sand and wooden cork.

PROCEDURE: Place the mixture in a beaker and add plenty of water. The sand particles sink, while the wooden corks float.

PERIOD 2: FROTH FLOTATION (FROSTATION)

This method is specifically used to separate an ore of a metal from earthy impurities.

PROCEDURE: The ore is crushed into powder and then mixed with water containing detergent, in order to cause frothing (foaming).

Air is then blown into the mixture so that the earthy impurities sink while the ore floats and mixes with the foam. The ore is finally recovered from the foam

PERIOD 3: PURE AND IMPURE SUBSTANCES: The following are the criteria for purity of chemical substances.

DENSITY: The density of a pure substance is definite and constant, while that of an impure substance higher than expected.

MELTING POINT: The melting point of a pure solid is sharp and definite. The presence of an impurity lowers the melting point of a substance, and spread its melting point over a wide range of temperature.

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