The table below lists examples of colloidal systems, most of which are very familiar. The dispersed phase describes the particles, while the dispersion medium is the material in which the particles are distributed.
Dispersion Medium. Another property of a colloidal system is the observed when the colloids are studied under a light microscope. The colloids scintillate, reflecting brief flashes of light because the colloidal particles move in a rapid and random fashion. This phenomenon, called Brownian motion, is caused by collisions between the small colloidal particles and the molecules of the dispersion medium.
Butter and mayonnaise are examples of a class of colloids called emulsions. An emulsion is a colloidal dispersion of a liquid in either a liquid or a solid. A stable emulsion requires an emulsifying agent to be present. Mayonnaise is made in part of oil and vinegar.
Since oil is nonpolar and vinegar is an aqueous solution and polar, the two do not mix and would quickly separate into layers. However, the addition of egg yolk causes the mixture to become stable and not separate.
Egg yolk is capable of interacting with both the polar vinegar and the nonpolar oil. The egg yolk is called the emulsifying agent.
Soap acts as an emulsifying agent between grease and water. Grease cannot be simply rinsed off your hands or another surface because it is insoluble.
Suspensions Suspensions are heterogeneous mixtures from which some of the particles settle with time. Muddy water is a classic suspension, with relatively large solid particles suspended in water. Upon standing the solids start to settle to the bottom of the container. In water suspensions the average suspended particle is larger than nm, whereas in a solution all particles are less than 1nm.
Suspensions are usually quite easy to separate into their components by filtration, with the larger particles being caught in the filter paper. Colloids Colloids are heterogeneous mixtures which do not settle out like suspensions, but are not true solutions either. Modern plastic paint is a typical colloid, with plastic particles less than nm but bigger than 1nm. These intermediate sized particles are big enough to scatter light, but small enough to remain suspended in the liquid.
When light is passed through a true solution, the dissolved particles are too small to deflect the light. However, the dispersed particles of a colloid, being larger, do deflect light see figure below. The Tyndall effect is the scattering of visible light by colloidal particles. You have undoubtedly "seen" a light beam as it passes through fog, smoke, or a scattering of dust particles suspended in air. All three are examples of colloids. Suspensions may scatter light, but if the number of suspended particles is sufficiently large, the suspension may simply be opaque, and the light scattering will not occur.
Listed in the table below are examples of colloidal systems, most of which are very familiar. Some of these are shown below see figure below. The dispersed phase describes the particles, while the dispersion medium is the material in which the particles are distributed. Butter and mayonnaise are examples of a class of colloids called emulsions. An emulsion is a colloidal dispersion of a liquid in either a liquid or a solid.
A stable emulsion requires an emulsifying agent to be present. Mayonnaise is made in part of oil and vinegar. Since oil is nonpolar, and vinegar is a polar aqueous solution, the two do not mix and would quickly separate into layers. In chemistry, a suspension is a heterogeneous mixture that contains solid particles sufficiently large for sedimentation.
A suspension is a heterogeneous mixture in which the solute particles do not dissolve, but get suspended throughout the bulk of the solvent, left floating around freely in the medium. A homogeneous mixture has the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions. A heterogeneous mixture consists of visibly different substances or phases.
Solutions have particles which are the size of atoms or molecules - too small to be seen. Is smoke a homogeneous or heterogeneous mixture or a pure substance? Homogeneous mixtures can't be filtered, but you can filter smoke OUT of the air, so it's not homogeneous. Examples of suspensions are: fine sand or silt in water or tomato juice.
Corn oil is homogeneous, White vinegar is homogeneous. A sugar solution is homogeneous since only a colorless liquid is observed.
A homogeneous mixture is a solid, liquid, or gaseous mixture that has the same proportions of its components throughout any given sample. Conversely, a heterogeneous mixture has components in which proportions vary throughout the sample. An example of a homogeneous mixture is air. Blood is a heterogeneous substance because the blood cells are physically separate from the blood plasma. The cells have different properties than the plasma. The cells can be separated from the plasma by centrifuging, which is a physical change.
The types of colloids includes sol, emulsion, foam, and aerosol. Sol is a colloidal suspension with solid particles in a liquid. Emulsion is between two liquids. Foam is formed when many gas particles are trapped in a liquid or solid. Aerosol contains small particles of liquid or solid dispersed in a gas. Blood is actually all three of the homogeneous mixtures.
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