When you combine two or more materials, you form a mixture. There are two categories of mixtures: homogeneous mixtures and heterogeneous mixtures. Here's a closer look at these types of mixtures and examples of mixtures.
Homogeneous mixtures appear uniform to the eye. They consist of a single phase, be it liquid, gas, or solid, no matter where you sample them or how closely you examine them.
Heterogeneous mixtures are not uniform. If you take two samples from different parts of the mixture, they will not have an identical composition. You can use a mechanical method to separate components of a heterogeneous mixture (e.g., sorting candies in a bowl). Sometimes these mixtures are obvious, where you can see different types of materials in a sample. For example, if you have a salad, you can see different sizes and shapes and types of vegetables. In other cases, you need to look more closely to recognize this mixture. Any mixture that contains more than one phase of matter is a heterogeneous mixture. Sometimes this can be tricky, because a change of conditions can alter a mixture. For example, an unopened soda in a bottle has a uniform composition and is a homogeneous mixture. Once you open the bottle, bubbles appear in the liquid. The bubbles from carbonation are gases, while the majority of the soda is liquid. An opened can of soda is an example of a heterogeneous mixture.
Examples of Mixtures
- Air is a homogeneous mixture. However, the Earth's atmosphere as a whole is a heterogeneous mixture. See the clouds? That's evidence the composition is not uniform.
- Alloys are made when two or more metals are mixed together. They usually are homogeneous mixtures. Examples include brass, bronze, steel, and sterling silver. Sometimes multiple phases exist in alloys. In these cases, they are heterogeneous mixtures. The two types of mixtures are distinguished by the size of the crystals that are present.
- Mixing together two solids, without melting them together, typically results in a heterogeneous mixture. Examples include sand and sugar, salt and gravel, a basket of produce, and a toy box filled with toys.
- Mixtures in two or more phases are heterogeneous mixtures. Examples include ice cubes in a drink, sand and water, and salt and oil.
- Liquid that are immiscible form heterogeneous mixtures. A good example is a mixture of oil and water.
- Chemical solutions are usually homogeneous mixtures. The exception would be solutions that contain another phase of matter. For example, you can make a homogeneous solution of sugar and water, but if there are crystals in the solution, it becomes a heterogeneous mixture.
- Many common chemicals are homogeneous mixtures. Examples include vodka, vinegar, and dishwashing liquid.
- Many familiar items are heterogeneous mixtures. Examples include orange juice with pulp and chicken noodle soup.
- Some mixtures that appear homogeneous at first glance are heterogeneous upon closer inspection. Examples include blood, soil, and sand.
- A homogeneous mixture can be a component of a heterogeneous mixture. For example, bitumen (a homogeneous mixture) is a component of asphalt (a heterogeneous mixture).
What Is Not a Mixture?
Technically, if a chemical reaction is occurring when you mix two materials, it's not a mixture... at least not until it has finished reacting.
- If you mix baking soda and vinegar, a chemical reaction occurs. Once the reaction has finished, the remaining material is a mixture.
- If you mix together ingredients to bake a cake, a chemical reaction occurs between the ingredients. While we use the term "mixture" in cooking, it doesn't always mean the same thing as the chemistry definition.
Learn more about the difference between homogeneous and heterogeneous mixtures.