A heterogeneous mixture is defined as a mixture that has a non-uniform composition. In other words, its composition varies from one location to another. In contrast, a homogeneous mixture has a uniform composition. Its appearance and composition are the same, no matter where you take a sample.
In chemistry, the difference between a homogeneous and heterogeneous mixture is a bit more complicated. A homogeneous mixture has a uniform composition with all components in a single phase, while a heterogeneous mixture has a non-uniform composition with components in at least two different phases.
Properties of Heterogeneous Mixtures
Heterogeneous mixtures display characteristic properties:
- A heterogeneous mixture contains two or more ingredients or phases. The phases might be at least two solids, liquids, or gases, or a solid/liquid (suspension), liquid/liquid (emulsion), gas/liquid (aerosol), or gas/solid (smoke).
- The different phases mix together, but are physically separate. In other words, they retain their own chemical identity.
- Samples taken from different parts of the mixture may have a different composition.
- It’s usually possible to separate components of a heterogeneous mixture.
10 Heterogeneous Mixture Examples
Here are 10 examples of heterogeneous mixtures:
- Cereal in milk is a great example of a heterogeneous mixture. It consists of a solid cereal in liquid milk.
- Oil and water form a heterogeneous mixture.
- Orange juice with pulp is a heterogeneous mixture. The components are unevenly distributed, plus they exist in two phases. Juice is a liquid and pulp is a solid.
- Sandy water is a heterogeneous mixture. It consists of two phases that readily separate.
- A pepperoni pizza is a heterogeneous mixture. You might get a pepperoni in one bite, yet not in another.
- Concrete is a heterogeneous mixture of cement, gravel, sand, and water.
- A chocolate chip cookie is a heterogeneous mixture. You may get different numbers of chocolate chips with each bite.
- A tossed salad is a heterogeneous mixture.
- A sandwich is a heterogeneous mixture.
- Ice cubes in a soda are a heterogeneous mixture. The ice and the soda are two distinct phases of matter (solid and liquid). Interestingly, soda before you open it appears to be homogeneous. Once you release the pressure, it’s heterogeneous because the gas bubbles and liquid are two phases. Let it go flat and it’s once again homogeneous.
Other examples include smoke, salad dressing, a mixture of sand and sugar, and gravel. In contrast, examples of homogeneous mixtures include air, salt water, and steel.
Heterogeneous vs Homogeneous Mixtures
Sometimes it’s obvious a mixture is heterogeneous, like a stream bed of different sizes, shapes, and colors of rocks. Other times, a mixture appears homogeneous from a distance, but is heterogeneous upon closer inspection. For example, if you look at sand on a beach, it may appear uniform. If you test many samples of the sand, they may have pretty much the same chemical composition. But, if you look at the sand under a magnifying glass, you can see it contains bits of shell, different minerals, and some organic matter.
Candy is another example. A bag of green M&Ms candies is truly homogeneous. Every candy you pull from the bag is green. A bag of regular M&Ms is heterogeneous, with each handful or sample containing a different selection of colors. But, the regular bag might appear homogeneous if you compare all the candies from 50 bags of candy to another 50 bags of candy. Statistically, they contain the same number of candies of each color.
The takeaway is that a mixture may appear homogeneous on a macroscopic scale, but become heterogeneous as you example smaller and smaller samples. Sometimes a heterogeneous mixture contains two phases that are the same state of matter, but if there are two states of matter, it’s a sure sign the mixture is heterogeneous.
Homogenization is a process that turns a heterogeneous mixture of non-soluble liquids into a homogeneous mixture. The most familiar example is homogenized milk. Milk straight from the cow separates into cream and milk. Homogenization breaks fat globules into smaller particles so milk doesn’t separate. Soft drinks, such as colas, are also homogenized. Pressurization of carbonated beverages not only produces bubbles when the drink is opened, but also keeps the ingredients evenly mixed during storage.
- IUPAC (1997). “Mixture.” Compendium of Chemical Terminology (the “Gold Book”) (2nd ed.). Oxford: Blackwell Scientific Publications. doi:10.1351/goldbook
- McClements, David J. (2008). “Lipid-Based Emulsions and Emulsifiers“. In Akoh, Casimir C.; Min, David B. (eds.). Food Lipids: Chemistry, Nutrition, and Biotechnology. Food Science and Technology (3rd ed.). Boca Raton, Florida: CRC. ISBN 978-1420046649.
- Whitten K.W.; Gailey K. D.; Davis R. E. (1992). General Chemistry (4th ed.). Philadelphia: Saunders College Publishing. ISBN 978-0-03-072373-5.