Chapter 15 Water and Aqueous Systems 15.3 Heterogeneous Aqueous 15.1 Water and Its Properties 15.2 Homogeneous Aqueous Systems 15.3 Heterogeneous Aqueous Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Why are some sunsets red? CHEMISTRY & YOU Why are some sunsets red? The atmosphere contains particles of water and dust. As sunlight passes through the particles, it is scattered. However, not all wavelengths are scattered to the same extent. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the difference between a suspension and a solution? Suspensions Suspensions What is the difference between a suspension and a solution? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the difference between a suspension and a solution? Suspensions Suspensions What is the difference between a suspension and a solution? A suspension is a mixture from which particles settle out upon standing. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

By contrast, the particle size in a solution is usually about 1 nm. Suspensions A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely. The particles in a typical suspension have an average diameter greater than 1000 nm. By contrast, the particle size in a solution is usually about 1 nm. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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 pass through filter paper. The particles of a suspension can be removed by filtration. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What distinguishes a colloid from a suspension and a solution? Colloids Colloids What distinguishes a colloid from a suspension and a solution? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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, throughout the dispersion medium, which can be a solid, liquid, or gas. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Some Colloidal Systems 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 Solid Marshmallow Emulsion Milk, mayonnaise Aerosol Fog, aerosol Smoke Dust in air Sols, gels Egg white, jelly, paint, blood, starch in water, gelatin Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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 larger particles of a suspension. They do not settle out with time. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Colloids The Tyndall Effect The scattering of visible light by colloidal particles is called the Tyndall effect. Flashlight Solution Colloid Suspension Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Suspensions also exhibit the Tyndall effect. Colloids Suspensions also exhibit the Tyndall effect. The particles in solutions are too small to scatter light. Flashlight Solution Colloid Suspension Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What would be the ideal conditions to see a red sunset? CHEMISTRY & YOU What would be the ideal conditions to see a red sunset? A misty or foggy evening would be ideal for seeing a red sunset. There would be a large number of particles to scatter the sunlight. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Colloids Brownian Motion Flashes of light, or scintillations, are seen when colloids are studied under a microscope. Colloids scintillate because the particles reflecting and scattering the light move erratically. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Colloids Brownian Motion The chaotic movement of colloidal particles, which was first observed by the Scottish botanist Robert Brown (1773–1858), is called Brownian motion. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

An emulsion is a colloidal dispersion of a liquid in a liquid. 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 maintaining the emulsion’s stability. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Oils and greases are not soluble in water. Colloids Emulsions 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Colloids Emulsions 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Properties of Solutions, Colloids, and Suspensions 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 Effect of gravity Stable, does not separate Unstable, sediment forms Filtration Particles not retained on filter Particles retained on filter Uniformity Homogeneous Heterogeneous Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

END OF 15.3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.