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15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Chapter 15

Water and Aqueous Systems

15.1 Water and Its Properties

15.2 Homogeneous Aqueous

Systems

(2)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

CHEMISTRY

CHEMISTRY & YOU

&

YOU

Why are some sunsets red?

The atmosphere

contains particles of

water and dust. As

sunlight passes

through the

particles, it is

(3)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Suspensions

Suspensions

Suspensions

(4)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Suspensions

Suspensions

Suspensions

What is the difference between a

suspension and a solution?

(5)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

A suspension differs from a solution

because the particles of a suspension

are much larger and do not stay

suspended indefinitely.

(6)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

A suspension differs from a solution

because the particles of a suspension

are much larger and do not stay

suspended indefinitely.

Suspensions

Suspensions

• The particles in a typical suspension have

an average diameter greater than 1000 nm.

• By contrast, the particle size in a solution is

(7)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Suspensions

Suspensions

• A solution is a homogeneous mixture.

• Suspensions are heterogeneous

(8)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Suspensions

Suspensions

The difference between a solution and suspension

is easily seen when the type of mixture is filtered.

The small size of the

solute particles in a

solution allows them to

(9)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

(10)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Explain why a mixture of sand and

water can be separated by filtration,

but a mixture of salt and water cannot.

(11)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Colloids

(12)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

A

colloid

is a heterogeneous mixture

containing particles that range in size

from 1 nm to 1000 nm.

• The particles are spread, or dispersed,

(13)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

The first substances to be identified as

colloids were glues.

Some Colloidal Systems

System

Type

Example

Dispersed

phase

Dispersion

medium

Gas

Liquid

Foam

Whipped cream

Gas

Solid

Foam

Marshmallow

Liquid

Liquid

Emulsion

Milk, mayonnaise

Liquid

Gas

Aerosol

Fog, aerosol

Solid

Gas

Smoke

Dust in air

Solid

Liquid

Sols, gels

(14)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

(15)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Colloids have particles smaller

than those in suspensions and

larger than those in solutions.

• These intermediate-sized particles cannot

be retained by filter paper as are the

(16)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

The Tyndall Effect

You cannot see a beam of sunlight

unless the light passes through particles

of water (mist) or dust in the air.

• These particles scatter the sunlight.

(17)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

The Tyndall Effect

(18)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

• Suspensions also exhibit the Tyndall

effect.

• The particles in solutions are too small

to scatter light.

(19)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

CHEMISTRY

CHEMISTRY & YOU

&

YOU

(20)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

CHEMISTRY

CHEMISTRY & YOU

&

YOU

What would be the ideal conditions to

see a red sunset?

(21)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Brownian Motion

Flashes of light, or scintillations, are

seen when colloids are studied under a

microscope.

(22)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Brownian Motion

The chaotic movement of colloidal

particles, which was first observed by

the Scottish botanist Robert Brown

(23)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Brownian motion is caused by collisions

of the molecules of the dispersion

medium with the small, dispersed

colloidal particles.

• These collisions help prevent the colloidal

particles from setting.

(24)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Coagulation

Colloidal particles also tend to stay

suspended because they become

charged by adsorbing ions from the

dispersing medium onto their surface.

(25)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Coagulation

All the colloidal particles in a particular

colloidal system will have the same

charge, although the colloidal system is

neutral.

• The repulsion between the like-charged

(26)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Coagulation

A colloidal system can be destroyed or

coagulated by the addition of

electrolytes.

• The added ions neutralize the charged

colloidal particles.

(27)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Emulsions

(28)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Emulsions

An

emulsion

is a colloidal dispersion of

a liquid in a liquid.

• An emulsifying agent is essential for the

formation of an emulsion and for

(29)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

Oils and greases are not soluble in

water.

However, oils and greases readily form

a colloidal dispersion if soap or

detergent is added to the water.

(30)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

• One end of a large soap or detergent

molecule is polar and is attracted to water

molecules.

• The other end of the soap or detergent

molecule is nonpolar and is soluble in oil or

grease.

• Soaps and other emulsifying agents thus

allow the formation of colloidal dispersions

between liquids that do not ordinarily mix.

(31)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Colloids

Colloids

This table summarizes the properties of solutions,

colloids, and suspensions.

Properties of Solutions, Colloids, and Suspensions

Property

System

Solution

Colloid

Suspension

Particle type

Ions, atoms,

small molecules

Large molecules or

particles

Large particles or

aggregates

Particle size

0.1–1 nm

1–1000 nm

1000 nm and larger

Effect of light

No scattering

Exhibits Tyndall effect Exhibits Tyndall effect

Effect of

gravity

Stable, does not

separate

Stable, does not

separate

(32)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Which of the following is a colloidal

system?

A.

mud

B.

gasoline

C.

blood

(33)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Which of the following is a colloidal

system?

A.

mud

B.

gasoline

(34)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Key Concepts

Key Concepts

A suspension differs from a solution

because the particles of a

suspension are much larger and do

not stay suspended indefinitely.

(35)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Glossary Terms

Glossary Terms

suspension:

a mixture from which

some of the particles settle out slowly

upon standing

colloid:

a mixture whose particles are

intermediate in size between those of a

suspension and a solute solution

(36)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

Glossary Terms

Glossary Terms

Brownian motion:

the chaotic

movement of colloidal particles, caused

by collision with particles of the solvent

in which they are dispersed

(37)

15.3 Heterogeneous Aqueous Systems >

15.3 Heterogeneous Aqueous Systems >

END OF 15.3

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