Suspensions. Ck12 Science. Say Thanks to the Authors Click (No sign in required)

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1 Suspensions Ck12 Science Say Thanks to the Authors Click (No sign in required)

2 To access a customizable version of this book, as well as other interactive content, visit AUTHOR Ck12 Science CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform. Copyright 2014 CK-12 Foundation, The names CK-12 and CK12 and associated logos and the terms FlexBook and FlexBook Platform (collectively CK-12 Marks ) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License ( licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the CC License ), which is incorporated herein by this reference. Complete terms can be found at Printed: July 31, 2014

3 C HAPTER Chapter 1. Suspensions 1 Suspensions Define suspension. Describe the properties and behavior of some typical suspensions. Why is the sea clear on some days, but not on others? On a calm day, the Caribbean Sea is clear and smooth. You can see deep into the water, deep enough to see fish and underwater plant life without obstruction. The situation changes markedly when a storm blows up. The sand on the bottom of the sea is stirred up, the water becomes turbid, and you can t see anything below the surface. The sand forms a suspension in the water that slowly clears up again after the storm blows over. Suspensions Take a glass of water and throw in a handful of sand or dirt. Stir it and stir it and stir it. The water may become turbid, or unclear. Have you made a solution? Sand and dirt do not dissolve in water and though it may look homogeneous for a few moments, the sand or dirt gradually sinks to the bottom of the glass. FIGURE 1.1 A suspension of dirt in water. A suspension is a heterogeneous mixture in which some of the particles settle out of the mixture upon standing. The particles in a suspension are far larger than those of a solution and thus gravity is able to pull them down out of the 1

4 dispersion medium (water). The typical diameter for the dispersed particles (the sand) of a suspension is about 1000 times greater than those of a solution (less than approximately two nanometers for particles in solution, compared to greater than 1000 nanometers for particles in suspension). Unlike in a solution, the dispersed particles can be separated from the dispersion medium by filtering. Suspensions are heterogeneous because at least two different substances in the mixture can be identified. Some Typical Aqueous Suspensions a. milk Milk is a complex mixture of water, proteins, fats, carbohydrates, and minerals. While the minerals and carbohydrates are water-soluble, the fats and some of the proteins do not dissolve but are held in suspension. b. paint Paint can either be water-based or use an organic solvent. For our discussion, we will limit ourselves to water-based paints. The materials will contain binders (organic polymers that help hold the paint to the surface of the material being painted). In addition, pigments are included to provide the desired color. Both the binders and the pigments are not water-soluble, so the paint must be stirred every time it is used. Paint that is allowed to sit for a long period of time will slowly begin to separate as the suspension of binders and pigments settles out. Summary Suspensions are heterogeneous mixtures. Some of the material in a suspension will settle out on standing. Solid material in a suspension can be removed by filtration. Practice Questions Use the link below to answer the following questions: 1. How large are particles in solution? 2. How large are particles in suspension? 3. Describe the appearance of a solution. 4. Describe the appearance of a suspension. Review Questions 1. Is a suspension a heterogeneous or a homogeneous mixture? 2. How can the solid material in a suspension be separated from the liquid? 3. Which part of milk is in suspension? 2 dispersion medium: The material in which the particles are distributed. suspension: A heterogeneous mixture in which some of the particles settle out of the mixture upon standing. turbid: Unclear, thick, or cloudy.

5 Chapter 1. Suspensions References 1. Courtesy of the US Navy. ves_crash_against_a_30-foot_cliff_at_cable_beach_located_on_the_southern_coastline_of_naval_station_- Guantanamo_Bay,_Cuba.jpg. 2. CK-12 Foundation - Joy Sheng.. 3