What Is a Heterogeneous Mixture? Definition and Examples

Heirloom tomatoes
This is a heterogeneous mixture of tomatoes.

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A heterogeneous mixture is a mixture having a non-uniform composition. The composition varies from one region to another, with at least two phases that remain separate from each other, with clearly identifiable properties. If you examine a sample of a heterogeneous mixture, you can see the separate components.

In physical chemistry and materials science, the definition of a heterogeneous mixture is somewhat different. Here, a homogeneous mixture is one in which all components are in a single phase, while a heterogeneous mixture contains components in different phases.

Examples of Heterogeneous Mixtures

  • Concrete is a heterogeneous mixture of an aggregate, cement, and water.
  • Sugar and sand form a heterogeneous mixture. If you look closely, you can identify tiny sugar crystals and particles of sand.
  • Ice cubes in cola form a heterogeneous mixture. The ice and the soda are two distinct phases of matter (solid and liquid). 
  • Salt and pepper form a heterogeneous mixture.
  • Chocolate chip cookies are a heterogeneous mixture. If you take a bite from a cookie, you may not get the same number of chips as you get in another bite.
  • Soda is considered a heterogeneous mixture. It contains water, sugar, and carbon dioxide, which forms bubbles. While the sugar, water, and flavorings may form a chemical solution, the carbon dioxide bubbles are not uniformly distributed throughout the liquid.

Homogeneous Versus Heterogeneous Mixtures

In a homogeneous mixture, the components are present in the same proportion, no matter where you take a sample. In contrast, samples taken from different parts of a heterogeneous mixture may contain different proportions of components. For example, if you take a handful of candy from a bag of green M&Ms, every candy you pick will be green. If you take another handful, once again all the candies will be green. That bag contains a homogeneous mixture. If you take a handful of candy from a regular bag of M&Ms, the proportion of colors you take might be different from what you get if you take a second handful. This is a heterogeneous mixture.

However, most of the time, whether a mixture is heterogeneous or homogeneous depends on the scale of the sample. Using the candy example, while you may get a different sample of candy colors comparing handfuls from a single bag, the mixture may be homogeneous if you compare all the colors of candies from one bag to all the candies from another bag. If you compare the ratio of colors from 50 bags of candy to another 50 bags of candy, chances are good there will be no statistical difference between the ratio of colors.

In chemistry, it is the same. On the macroscopic scale, a mixture may appear homogeneous, yet become heterogeneous as you compare the composition of smaller and smaller samples.

Homogenization

A heterogeneous mixture can be made into a homogeneous mixture via a process called homogenization. An example of homogenization is homogenized milk, which has been processed so that the milk components are stable and don't separate. In contrast, natural milk, while it might appear homogeneous when shaken, isn't stable and readily separates into different layers.