A heterogeneous mixture is simply any mixture that is not uniform in composition — it's a non-uniform mixture of smaller constituent parts. By contrast, a mixture that is uniform in composition is a homogenous mixture. For the purposes of this discussion, “not uniform” means anything that clearly has different parts visible to the naked eye or that could be easily separated from each other. You can find many examples of heterogeneous mixtures in solid, liquid and gaseous form throughout nature.
The whole world is a solid heterogeneous mixture! Solid heterogeneous mixtures can contain liquid or gaseous components, but as a whole, they act like solids.
- mixed nuts - Mixed nuts at a party are a type of heterogeneous mixture, which can be separated into individual parts. Simply sort the mixture into separate piles for each type of nut, and you have broken down a heterogeneous mixture into its component parts.
- rocks in sand - Rocks in the sand at the beach are a heterogeneous mixture. Natural processes have mixed up sand, stones, shells, and even living things, scattering them across the beach as a mixture.
- salad - A salad with lettuce, cheese, seeds, tomatoes, broccoli, and other vegetables is an example of a heterogeneous mixture. Each different piece of the salad can be separated into different parts with minimal effort.
- soil - Soil is an example of a heterogeneous mixture. It combines many different components which are not uniform, such as stone, clay, decaying plant material, and even living things.
When a mixture contains multiple distinct components, but the whole mixture acts like a liquid, that is a liquid heterogeneous mixture. Here are some examples:
- vinaigrette salad dressing - A bottle of balsamic vinaigrette salad dressing is a mixture that is heterogeneous, consisting primarily of oil and vinegar. You can (and should!) shake up a vinaigrette to make the mixture appear and taste more combined, but it will always separate into its component parts when left alone.
- ice cubes in a drink - When you first put ice cubes into a glass of water or tea, it is a heterogeneous mixture. There are two distinct parts, the ice and the tea or water.
- oil and water - When you put oil and water together they do not mix. Therefore, these are a heterogeneous mixture since they are two separate parts.
- mud puddle - Mud puddles are a heterogeneous mixture. Dirt, leaves and all sorts of other runoff mixes with rainwater and pools into a mixture where the component parts can be clearly seen or separated.
Some heterogeneous mixtures are primarily gaseous. Gaseous mixtures may contain liquids or even solids, but as a whole, they act like a gas.
- fog - Mist and fog can be considered heterogeneous mixtures, as tiny droplets of water hang visibly in the air. You can see and walk through the fog.
- smog - Smog is a heterogeneous mixture of various particles and pollutants suspended in the air. The dirty particles that make up the smog can be removed from the air and breathed into the lungs, making smog quite a problematic heterogeneous mixture.
- smoke - Smoke from a fire is another heterogeneous mixture, combining chemicals from the fire’s fuel and CO2 from the oxidation process with the air surrounding the flame.
- clouds - You can see clouds in the sky because it's a heterogeneous mixture. Water vapor goes up into the sky and mixes with air creating visible clouds.
While almost all heterogeneous mixtures contain some substances in different phases, many are defined by the presence of things in distinct, different phases of matter.
- bowl of cereal - The classic chemistry class example of a multi-phase mixture is a bowl of cereal. Here you have a heterogeneous mixture of solid cereal in liquid milk.
- carbonated liquid - Carbonated water (or carbonated anything) is a multi-phase heterogeneous mixture, with gaseous carbon dioxide (CO2) bubbling through liquid water (H2O).
- lava - Lava from a volcano is a multi-phase mixture, with some solid chunks of rock surrounded by hot, molten stone. It might be too hot to touch, but it has distinctly separate parts.
- sand and water - If you put sand and water into a glass and let them settle, you will see the sand at the bottom and water at the top. That's because they don't mix.
Heterogeneous mixtures (mixtures where you can see the different parts) are distinctly different from homogeneous mixtures that create a uniform mixture. To help to understand these two concepts, a heterogeneous mixture is like hot cocoa with marshmallows floating in it. They are mixed together, but the marshmallows are visible by your eyes. A homogenous mixture would be the hot cocoa itself. The water, cocoa and sugar have all mixed together to create a uniform mixture without any smaller or larger parts.
Most heterogeneous mixtures contain multiple parts in multiple phases, but they usually behave on the whole as if they belong to one particular phase of matter:
- solid mixture - mixture with a firm and stable shape
- liquid mixture - a mixture that flows freely
- gaseous mixture - mixture no fixed shape and expands freely to fill space
There are other phases of matter, including plasma and Bose-Einstein condensates, but they’re beyond the scope of this article.
Homogeneous and heterogeneous mixtures are just the simplest, most straightforward way mixtures are defined in science. Things get more interesting as they get more specific.
- suspensions - solid particles that float in a liquid or gas
- solutions - homogeneous mixtures in which one substance, the solute, dissolves perfectly into another, the solvent
- colloids - tiny unmixable droplets float in a different substance
- emulsions - liquid colloids in which droplets of an unmixable liquid float in another
All these mixtures are a part of daily life. Examples can be found in your kitchen, your car and your own human body. Understanding what mixtures are and how science defines them is an important part of learning how the world works. When you’re prepared to perform some scientific experiments of your own, be sure to follow the scientific method. It’s the official process for testing hypotheses!