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FIND OUT MORE. Chemical Industry 206–207 • Kidneys 147 • Matter 156 • Mixtures 172

Science and Technology^173

Filtration is a method of separating a solid from a liquid by

trapping solid particles in a material that only lets the liquid

through. A coffee filter separates solid coffee grounds from liquid

coffee. The size of the pores (holes) in the filter paper determines

which particles will pass through.

HOW DOES DISTILLATION WORK?

When a liquid mixture is heated, the liquid with the

lower boiling point evaporates (becomes a vapour),

leaving behind the liquid with the higher boiling

point. Cooling condenses the vapour back to liquid.

Fractional distillation separates substances one

by one as the temperature rises.

WHAT IS A CENTRIFUGE?

A centrifuge is a spinning machine (like a spin

dryer) that separates materials. A mixture of

liquids and solids is spun at high speed in a tube.

The larger, denser particles sink and collect at the

bottom. Light particles collect at the top. Blood

cells are separated from plasma (the liquid part

of blood) by this method.

WHAT IS DIALYSIS?

Your kidneys clean your blood. Waste chemicals

dissolved in the blood pass through a membrane to

be excreted in urine. Blood cells are too big to pass

through and are retained in the body. If a patient's

kidneys fail they can be treated on a dialysis machine.

This uses a synthetic membrane outside the body.

How do we extract salt from sea water? Methods for

separating a mixture depend on differences in the

physical properties of its components.

HOW CAN SOLIDS BE SEPARATED?

Differences in size, density, solubility, and magnetic

properties separate one solid from another. Adding

water separates salt from sand – the salt dissolves, the

sand does not.. FILTRATION separates an insoluble

solid (one that does not dissolve) from a liquid.

HOW ARE GASES SEPARATED?

Air is separated to produce nitrogen, oxygen, and

other gases by first cooling it to the liquid state at

-196°C (-321°F). The liquid air is fractionally distilled.

Gases may also be separated by the rate they diffuse

through a barrier. Light molecules diffuse more

quickly than heavy molecules.

4 LABORATORY DISTILLATION

In this laboratory demonstration,

the solution to be distilled is

boiled by a Bunsen burner. Vapour

from the boiling liquid is directed

into a water-cooled condenser.

The condenser is angled so that

gravity causes the condensed

liquid (turned from vapour back

to liquid by cooling) to run down

into the collecting flask.

Separating Mixtures

FILTRATION

CENTRIFUGE 3

A blood sample in a microtube is

placed into a centrifuge. The

high-speed rotation separates the

blood components into layers

ready for analysis.

PANNING FOR

GOLD 3

Gold is separated

from gravel. Gold is

heavier and sinks more

quickly to settle in the

bottom of the pan.

Vapour condenses

and liquid runs into

collecting flask

Vapour rises
as water in the
mixture boils

Hot water

vapour enters

the condenser’s

inner tube

Water boils
at 100°C (212°F)

Cold water is fed

into the condenser’s

outer tube

Water is led

off from the

outer tube

Bunsen

burner

gives heat

Sodium
dichromate
and water

separating

mixtures