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Chemistry 15.3

Chemistry 15.3. Slide 1 of 21. Heterogeneous Aqueous Systems. 15.3.

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Chemistry 15.3

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  1. Chemistry 15.3 Slide 1 of 21

  2. 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.

  3. 15.3 Suspensions • Suspensions • What is the difference between a suspension and a solution?

  4. 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.

  5. 15.3 Suspensions • Suspensions are heterogenous because at least two substances can be clearly identified.

  6. 15.3 Colloids • Colloids • What distinguishes a colloid from a suspension and a solution?

  7. 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.

  8. 15.3 Colloids • Colloids have particles smaller than those in suspensions and larger than those in solutions.

  9. 15.3 Colloids

  10. 15.3 Colloids • The Tyndall Effect • The scattering of visible light by colloidal particles is called the Tyndall effect.

  11. 15.3 Colloids • Particles in colloids and suspensions reflect or scatter light in all directions. Solutions do not scatter light.

  12. 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.

  13. 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.

  14. 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. 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.

  16. 15.3 Colloids

  17. 15.3 Section Quiz. • 15.3.

  18. 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.

  19. 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.

  20. 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.

  21. Concept Map 15 • Concept Map 15 Solve the Concept Map with the help of an interactive guided tutorial.

  22. END OF SHOW

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