When you combine two or more materials, you form a mixture. In chemistry, a mixture is a combination that does not produce a chemical reaction; in other words, each substance in the mixture retains its own chemical identity. There are two categories of mixtures: hom*ogeneous mixtures and heterogeneous mixtures. Here's a closer look at these two types of mixtures, along with examples of each.
Key Takeaways: Mixture
- A mixture is formed by combining two or more materials.
- A hom*ogeneous mixture appears uniform, regardless of where you sample it. A heterogeneous mixture contains particles of different shapes or sizes, and the composition of one sample may differ from that of another sample.
- Whether a mixture is heterogeneous or hom*ogeneous depends on how closely you examine it. Sand may appear hom*ogeneous from a distance, yet when you magnify it, it is heterogeneous.
- Examples of hom*ogeneous mixtures include air, saline solution, most alloys, and bitumen.
- Examples of heterogeneous mixtures include sand, oil, water, and chicken noodle soup.
hom*ogeneous Mixtures
hom*ogeneous mixtures appear uniform to the eye. No matter how closely you examine them, you won't be able to see individual chemicals or ingredients in this type of mixture. Because they are uniform and consistent, they only consist of a single phase of matter—be it solid, liquid, or gas. The chemical composition is the same for any sample of the mixture.
Heterogeneous Mixtures
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 or filtering rocks to separate them from sand).
How to Tell Whether a Mixture is Heterogeneous or hom*ogeneous
Sometimes classifying mixtures is obvious, especially if you can see different types of materials in a sample. For example, if you have a salad, you can see different sizes, shapes, and types of vegetables. In other cases, you need to look more closely to recognize the type of mixture. Any mixture that contains more than one phase of matter is heterogeneous.
On the other hand, sometimes it's tricky to determine the type of mixture because a change in conditions can alter a mixture. For example, an unopened soda in a bottle has a uniform composition and is a hom*ogeneous mixture. Once you open the bottle, bubbles appear in the liquid. The bubbles from carbonation are gasses, 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 hom*ogeneous 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 hom*ogeneous 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 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.
- Immiscible liquids are those that can't mix together. As a result, they form heterogeneous mixtures. A good example is a mixture of oil and water.
- Chemical solutions are usually hom*ogeneous mixtures. The exception would be solutions that contain another phase of matter. For example, you can make a hom*ogeneous solution of sugar and water, but if there are crystals in the solution, it becomes a heterogeneous mixture.
- Many common chemicals are hom*ogeneous 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 hom*ogeneous at first glance are heterogeneous upon closer inspection. Examples include blood, soil, and sand.
- A hom*ogeneous mixture can be a component of a heterogeneous mixture. For example, bitumen (a hom*ogeneous mixture) is a component of asphalt (a heterogeneous mixture).
Not a Mixture
Technically, if a chemical reaction occurs when you mix two materials, it's not a mixture—at least not until it has finished reacting.
For example, if you mix baking soda and vinegar, a chemical reaction occurs. Once the reaction has finished, the remaining material is a mixture. Similarly, if you mix 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.
