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By the end of this section, you will be able to:
  • Describe the composition and properties of colloidal dispersions
  • List and explain several technological applications of colloids

As a child, you may have made suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water, known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles that are visible (or that can be seen with a magnifying glass). They are cloudy, and the suspended particles settle out after mixing. On the other hand, when we make a solution, we prepare a homogeneous mixture in which no settling occurs and in which the dissolved species are molecules or ions. Solutions exhibit completely different behavior from suspensions. A solution may be colored, but it is transparent, the molecules or ions are invisible, and they do not settle out on standing. A group of mixtures called colloids (or colloidal dispersions ) exhibit properties intermediate between those of suspensions and solutions ( [link] ). The particles in a colloid are larger than most simple molecules; however, colloidal particles are small enough that they do not settle out upon standing.

This figure contains three photos and correponding particle diagrams. In a, a photo of an aquarium containing fish is shown. The particle diagram beneath it shows 90 tiny red spheres. In b, a photo is shown of milk being poured into a cup. The corresponding particle diagram shows about 25 medium sized red spheres.In c, a photo is shown of two pairs of sandal clad feet in mud. The particle diagram below shows 10 fairly large red spheres.
(a) A solution is a homogeneous mixture that appears clear, such as the saltwater in this aquarium. (b) In a colloid, such as milk, the particles are much larger but remain dispersed and do not settle. (c) A suspension, such as mud, is a heterogeneous mixture of suspended particles that appears cloudy and in which the particles can settle. (credit a photo: modification of work by Adam Wimsatt; credit b photo: modification of work by Melissa Wiese; credit c photo: modification of work by Peter Burgess)

The particles in a colloid are large enough to scatter light, a phenomenon called the Tyndall effect    . This can make colloidal mixtures appear cloudy or opaque, such as the searchlight beams shown in [link] . Clouds are colloidal mixtures. They are composed of water droplets that are much larger than molecules, but that are small enough that they do not settle out.

This is a photo of searchlight beams in the night sky of a city scene.
The paths of searchlight beams are made visible when light is scattered by colloidal-size particles in the air (fog, smoke, etc.). (credit: “Bahman”/Wikimedia Commons)

The term “colloid”—from the Greek words kolla , meaning “glue,” and eidos , meaning “like”—was first used in 1861 by Thomas Graham to classify mixtures such as starch in water and gelatin. Many colloidal particles are aggregates of hundreds or thousands of molecules, but others (such as proteins and polymer molecules) consist of a single extremely large molecule. The protein and synthetic polymer molecules that form colloids may have molecular masses ranging from a few thousand to many million atomic mass units.

Analogous to the identification of solution components as “solute” and “solvent,” the components of a colloid are likewise classified according to their relative amounts. The particulate component typically present in a relatively minor amount is called the dispersed phase    and the substance or solution throughout which the particulate is dispersed is called the dispersion medium    . Colloids may involve virtually any combination of physical states (gas in liquid, liquid in solid, solid in gas, etc.), as illustrated by the examples of colloidal systems given in [link] .

Questions & Answers

What is saturated hydrocarbon?
Ebenezer Reply
Alkane series are saturated Hydrocarbon
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Emmanuel Reply
What is acid
is agroup of substance that relaise hydrogen ion in the water solution.
An acid is a proton donor or an electron pair acceptor
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Mercy Reply
Maybe by reading proofs or practical work and application in modern world.
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Samuel Reply
whats de shape of water
Amara Reply
water has no shape because it's liquid
water is a shapeless, odourless, colourless and tasteless substance that only takes the shape of its container.
i think they're referring to the molecular shape?
It has no shape but takes the shape of the container
Yeah I think so too and it's a bent shape
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Wilson Reply
what is the meaning of STP
introduction to chemistry for beginner
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through out human history
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is euglena a unicellular organ
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is euglena a unicellular organism
how is hydrogen can be heated
Buwembo Reply
what is difference between atom and molecule
Aqeela Reply
Atom is the smallest part of matter; it consists of equal number of protons and electrons. It may have neutrons. A molecule is a compound made of atoms covalently bonded.
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Mercy Reply
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kolawole Reply
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what's an atom?
Davy Reply
it's the smallest unit of Matter
smallest part of an element
also, depending on its (atom's) structure, that is the amount of protons and neutrons and electrons, is the determining factors of what element it is.
is a smallast particals of an element
it is the smallest part of an element that can take part in a chemical reaction
is the smallest part of an element
An atom is the smallest indivisible part of a matter
Practice Key Terms 8

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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