homework encyclopedia

FIND OUT MORE. Chemistry 162 • Heat 168–169 • Matter 156 • Soil 48

172 Science and Technology

A mixture is a jumble of different

things. Soil is a mixture of sand,

clay, stones, roots, and plant and

animal remains. The air is a mixture

of different gases. Sea water contains

a mixture of different chemical

compounds in. SOLUTION.

WHAT IS A RANDOM WALK?

The movement of a single molecule in a

liquid or a gas is a zig-zag random walk.

The molecule is continually moving and

changing direction as it collides with other

molecules. A group of molecules that were

concentrated in one spot gradually spread

apart. This explains how an odour, for example

perfume, spreads through a room.

WHY DON’T OIL AND WATER MIX?

Oil is insoluble (does not dissolve) in water because oil

and water molecules repel each other. Cooking oil and

water can be physically mixed together by shaking

them vigorously in a bottle, but when the mixture

is left to stand, the oil and water molecules gradually

separate again. Oil is less dense (heavy) than water,

so the oil floats on top of the water.

DO SOLIDS, LIQUIDS, AND GASES MIX?

All the states of matter can mix, with themselves and

each other. Solid powders mix easily. Most rocks are a

mixture of different minerals. Some liquids mix easily,

and some don’t. Water and alcohol mix together, but

water and oil do not mix. Gases mix rapidly by

. DIFFUSION – their molecules can move between
each other because gas molecules are widely spaced.

WHY IS IT EASIER TO MIX THAN TO SEPARATE?

It couldn’t be easier to mix a bucket of red balls with

a bucket of white balls – just tip them together.

Mixing makes the balls more jumbled. Scientists say

that they have more entropy (disorder). Separating the

balls is much harder. To make them ordered again,

red balls in one bucket, white in another, you have

to pick the balls out one at a time.

A solution is a mixture in the liquid state.

Molecules of one substance are dispersed

(scattered) throughout molecules of another

– the substance is dissolved. The amount of

a substance that will dissolve in another is

called its solubility.

WHAT IS THE DIFFERENCE BETWEEN A MIXTURE

AND A COMPOUND?

The components of a mixture are physically mixed

together, but they have not reacted chemically. When

materials react chemically, chemical bonds break and

reform, producing compounds with new properties.

When two liquids or gases are in the same

container, the random motion of their

molecules makes them mingle together

until the mixture is the same

throughout. This is called diffusion.

4 MIXING BY DIFFUSION

Crystals of potassium

permanganate dissolve in water,

producing a dark purple

solution. Even without

stirring, the purple

solution spreads

gradually through

the clear water

in the flask.

Mixtures

Lamp base contains an electric

bulb. This heats the bubbles. The

liquid nearer the heat expands,

becomes less dense, and rises

DIFFUSION

SOLUTION

4 LAYERS OF OIL AND WATER

Oil and water don’t mix, and therefore do not form a solution.

4 LAVA LAMP

The lamp contains two liquids

with slightly different densities

that do not mix.

Liquid bubbles

expand and float up

Warm bubbles rise,

cool, and sink again

Potassium

permanganate

diffuses into

the water

Potassium

permanganate

crystals

y) ,

mixtures