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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

A 45 ml of ph=1,hcl was reacted with a 55l ml of ph=13, naoh solution . what is the final ph
chamini Reply
what is coordination number
YERUMAKULA Reply
coordination number is the number of atoms or ions immediately surrounding a central atom in a complex or crystal
Chidera
what is isotope
Bukar
who is the father of chemistry
Roland Reply
Antoine Lavoisier. Father of modern chemistry
Yapi
What is geometric isomerism
Imoh Reply
jo
Lakshmi
pls I don't really know teach me
Joel
geometric isomerism are molecules that are locked into their spatial position with respect to one another due to a double Bond or ring structure
Chidera
Chromatography is a physical method of seperation where by mixtures that are in two phrases are separated
Lexzzy Reply
What is chromatography?
Chukwudi Reply
meaning of electrode
DJKRANKY Reply
is ion exchange and ion chromatography the same process?
Vivian
define boyes law and give the formula
Esther Reply
define chemistry and it's properties
Esther
Boyle's law state that at a constant temperature, the pressure of a fixed mass of gas is inversely proportionally to it's volume. P=k/v P1v1=p2v2
MAUREE
Chemistry is the study of matter and it's properties..... It's deals with the composition that governors d use of matter..... Chemistry is also d study of chemical reaction of a substance and it's matter. Properties of chemistry Atom Elements Compound Molecules
MAUREE
chemistry seems more accurately defined as the measurement and study of the interaction / behavior that occurs between any given person place or thing or unit of measure, ie time and energy correlation
Elaine
Reactive metals are extracted by _______?
Joseph Reply
electrolytic reduction
Amisu
what is ionxide
Wisdom Reply
What is isometrics
Kamaluddeen Reply
Molar mass of aluminum
Victor Reply
why an equation should balanced?
Kwanele Reply
in order to obey the law of conservation of mass
Ibrahim
why does the atomic radius increase across the period
Timothy Reply
preparation of hydrogen in the laboratory
Emmanuel Reply
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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