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In this overview of heterogeneous aqueous systems, explore the differences between colloids and suspensions. Learn from the example of astronaut Shannon Lucid sharing gelatin, a colloidal mixture, with her Russian crewmates. Understand key concepts such as the Tyndall effect, the chaotic movement of colloidal particles known as Brownian motion, and the coagulation process in colloids. Additionally, discover the role of emulsifying agents in stabilizing emulsions, like mayonnaise. Test your knowledge with a section quiz covering these fundamental topics in chemistry.
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Chemistry 15.3 Slide 1 of 21
Heterogeneous Aqueous Systems 15.3 • In 1996, American astronaut Shannon Lucid shared a gelatin dessert with her Russian crewmates. Gelatin is a heterogeneous mixture called a colloid. You will learn more about the characteristics of colloids and a related mixture called a suspension.
15.3 Suspensions • Suspensions • What is the difference between a suspension and a solution?
15.3 Suspensions • A suspension is a mixture from which particles settle out upon standing. • A suspension differs from a solution because the particles of a suspension are much larger and do not stay suspended indefinitely.
15.3 Suspensions • Suspensions are heterogenous because at least two substances can be clearly identified.
15.3 Colloids • Colloids • What distinguishes a colloid from a suspension and a solution?
15.3 Colloids • A colloid is a heterogeneous mixture containing particles that range in size from 1 nm to 1000 nm. The particles in a colloid are spread throughout the dispersion medium.
15.3 Colloids • Colloids have particles smaller than those in suspensions and larger than those in solutions.
15.3 Colloids
15.3 Colloids • The Tyndall Effect • The scattering of visible light by colloidal particles is called the Tyndall effect.
15.3 Colloids • Particles in colloids and suspensions reflect or scatter light in all directions. Solutions do not scatter light.
15.3 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. • Brownian motion is caused by collisions of the molecules of the dispersion medium with the small, dispersed colloidal particles.
15.3 Colloids • Coagulation • A colloidal system can be destroyed, or coagulated, by the addition of ions having a charge opposite to that of the colloidal particles. • The added ions neutralize the charged colloidal particles. The particles can clump together to form heavier aggregates and precipitate from the dispersion.
15.3 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.
15.3 Colloids • Mayonnaise is heterogeneous mixture of oil and vinegar. Such a mixture would quickly separate without the presence of egg yolk, which is the emulsifying agent.
15.3 Colloids
15.3 Section Quiz. • 15.3.
15.3 Section Quiz. • 1. One characteristic that is unique to a suspension is that the particles in it • settle due to gravity. • are too small to be seen. • cannot be filtered. • produce the Tyndall effect.
15.3 Section Quiz. • 2. Homogenized milk contains finely divided particles that do not settle out rapidly and are not readily filtered. Thus, homogenized milk is a • colloid. • substance. • suspension. • solution.
15.3 Section Quiz. • 3. The scattering of light known as the Tyndall effect can be seen in • emulsions and solutions. • colloids and suspensions. • solutions and suspensions. • colloids and solutions.
Concept Map 15 • Concept Map 15 Solve the Concept Map with the help of an interactive guided tutorial.
