Chemistry: Shake It Up: Mixtures

Shake It Up: Mixtures

Mixtures are materials that contain more than one type of pure element or compound. For example, even if cockroaches haven't been crawling around on it, potato salad is referred to as being a mixture because the potatoes are made of different chemical compounds than the mayonnaise. Likewise, salt water is a mixture because it consists of pure sodium chloride ("salt") mixed with pure water.

Molecular Meanings

When two pure substances are mixed evenly, the resulting material is referred to as a homogeneous mixture, also known as a solution.

The components in a mixture may or may not exist within the same phase. For example, if we are talking about a mixture of two solids, each solid may be distinctly different from one another, such as you'd find in a bowl of gumdrops where each gumdrop is different from the others. In a mixture of two liquids, there may or may not be more than one phase—generally, liquids tend to dissolve in one another, and it's uncommon to find mixtures of more than two or three liquids that don't dissolve one another, called multiphase liquid mixtures. An example of a multiphase liquid mixture would be oil and vinegar. Mixtures of gases are always well mixed and don't readily separate into separate phases. An example of a gaseous mixture would be air, in which the oxygen, nitrogen, and other stuff don't separate into separate components.

Homogeneous Mixtures

Molecular Meanings

Mixtures are said to be heterogeneous if they contain two or more unevenly mixed parts.

We've already seen that elements and compounds are homogeneous materials because they have a completely uniform composition. Some mixtures can also be said to be homogeneous because they contain two or more pure substances mixed together in a uniform fashion. These mixtures are called, straightforwardly enough, homogeneous mixtures.

You've Got Problems

Problem 1: Identify each of the following as being either a homogeneous or heterogeneous mixture:
(a) turkey stuffing
(b) sugar water
(c) ice cream cone

You can usually tell if something is a homogeneous mixture by looking at it. If something contains more than one pure material and appears uniform to the naked eye, it's probably a homogeneous mixture. Examples of homogeneous mixtures include salt water, air, and stainless steel.

Heterogeneous Mixtures

Most of the things that we encounter in our everyday lives aren't evenly mixed. For example, I had a jelly-filled doughnut with powdered sugar on it for breakfast this morning. When I bit into it, the powdered sugar went all over my face and the jelly plopped into my lap. Because the material separated into several distinct parts, the doughnut could be said to be a heterogeneous mixture.

Heterogeneous mixtures are pretty easy to spot because they clearly contain several different components. Examples of heterogeneous mixtures include my shoe, that annoying dirt-eating kid down the street, and the 1987 Boston Red Sox.

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Excerpted from The Complete Idiot's Guide to Chemistry © 2003 by Ian Guch. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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