Mixtures and Solutions

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Hello, I am haveing some confusions with homogeneous mixtures and solutions. I can't really see the difference and I would like to know how to distinguish between the two for the kids.

-- Deanna Zapata (deebo_100@yahoo.com), December 17, 2000


Hi Deanna:

There are three basic types of mixtures.

Suspensions are heterogeneous mixtures in which the one of the substances consists of particles that are too large to remain completely mixed and therefore “settle out.” Muddy water and dusty air are classic examples.

Colloids are mixtures in which one of the substances consists of particles that are sufficiently small to remain mixed: i.e., they do not settle out. These particles are usually aggregates or clumps of atoms, ions, or molecules. My chemistry textbook classifies colloids as “heterogeneous” mixtures, but I believe that Prentice Hall incorrectly calls them “homogeneous mixtures,” which is probably causing some of your confusion. I will define homogeneous and heterogeneous below.

A solution is a mixture in which the particles of both substances are uniformly dispersed as separate atoms, ions, or molecules.

Heterogeneous mixtures: The components are not evenly mixed. Suspensions are obviously not evenly mixed: One can see this with the naked eye. Colloids appear evenly mixed, but upon close inspection one will observe the aforementioned aggregates of one substance, which are by definition not evenly mixed (read on).

Homogeneous mixtures: the components are evenly mixed. Look anywhere in the substance (top, bottom, left right, even looking at point A and point B anywhere in the mixture) and you will find a uniform distribution of the different substances. You will not find one of the substances clumped together in one place, as you will with a colloid. Think of fog, for example (a colloid). The water droplets in fog are not individual water molecules: They are (relatively) large clumps of water molecules, therefore one cannot say that the water molecules are evenly mixed in the air.

So, in effect, homogeneous mixtures and solutions are the same thing, as I understand the terms.

Reference: Chemistry, by Stanley R. Radel and Marjorie H. Navidi, 2nd Edition

Let me know if I have confused you further…Mike

-- Michael Gatton (mwgatton@hotmail.com), December 17, 2000.

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