Chemistry, Third edition

Separating Mixtures

Objectives

Describes the techniques used by chemists to separate mixtures

Demonstrates how to separate solids from solutions or suspensions,

liquids from mixtures of liquids and solids from solid mixtures

Explains what is meant by the terms ion exchange and solvent extraction

Discusses the various types of chromatography

Often in practical chemistry, only one substance is needed from a mixture of sub-

stances. The substance has to be separatedfrom the mixture.

Separating a solid from a liquid

A solid that is mixed with a liquid may be insolublein the liquid, or it may have dis-

solved. When an insoluble solid floats in a liquid, the mixture is called a suspension.

Insoluble solids

Insoluble solids can be separated by filtration.

The solid is trapped by the filter paper, while

the liquid passes through it. A simple example

of this technique is the separation of a mix-

ture of fine sand in water. A residue of sand

collects in the filter paper and the liquid that

drips through (in this case water) is called the

filtrate. This type of filtration is called gravity

filtration(Fig. 19.1).

Small amounts of a fine suspension can be

separated in a centrifuge. Tubes of the suspen-

sion are spun around very quickly and the

solid collects at the bottom of the tube, leaving

clear liquid at the top. The clear liquid can

then be removed with a pipette, leaving the

solid in the tube (Fig. 19.4).

19.1

Contents

19.1Separating a solid
from a liquid 350

19.2Separating two
liquids 353

19.3Separating solids 355

19.4Steam distillation 356

19.5Ion exchange 356

19.6Solvent extraction 357

19.7Chromatography 360

19.7Revision questions 364

Mixture

of sand

and water

Sand

Filter paper

in funnel

Water

Glass rod

Fig. 19.1Gravity filtration.

19

UNIT