In chemistry, mixtures come in two overarching categories: heterogeneous mixtures and homogeneous mixtures. We've covered heterogeneous mixtures in depth right here, but what about homogeneous mixtures? A homogeneous mixture is simply any mixture that is uniform in composition throughout. As long as each substance is mixed in enough to be indistinguishable from the others, it is a homogeneous mixture.
One of the most interesting facts about heterogeneous and homogeneous mixtures is that, in a sense, there's no real distinction. Look closely enough at any substance, even a pure element, and it becomes heterogeneous because it's made up of different subatomic particles. Conversely, at a large enough scale everything in the universe is homogeneous, because it becomes impossible to differentiate components.
The properties of homogeneous mixtures are best defined on a scale somewhere between the two. Scientists (and we) most often use the simple standard of the naked eye. If a substance can be seen to contain two or more distinct components, it is considered heterogeneous. If it appears to be just one uniform substance, it's homogeneous.
Here follow several examples of homogeneous mixtures.
There is a wide variety of solid homogeneous mixtures, from naturally occurring materials like stone to synthetic plastics.
Bitumen, the solid form of petroleum and source of gasoline, diesel and other fossil fuels, is a homogeneous mixture of complex hydrocarbon chemicals.
Cement is a solid homogeneous mixture of calcium compounds. Mixed with sand, gravel and water, it becomes concrete, one of the most important building materials in the world.
Many alloys are homogeneous mixtures of metals, or of a metal and a nonmetallic substance. Bronze, which is made from copper and tin, is an example of the first kind of alloy. Steel, made from iron and carbon, is an example of the second.
Plastics are some of the world's most important homogeneous mixtures. The discovery that certain mixtures of synthetic organic compounds could be made into solid objects changed the entire manufacturing industry.
Many of the liquids you encounter every day - indeed, most of the liquids that power your body - are examples of homogeneous mixtures.
In the human body, blood plasma is an example of a homogeneous mixture. The colorless fluid holds blood cells in suspension. It makes up a little more than half of the volume of human blood.
Milk is a homogeneous colloid. Colloids are mixtures that consist of tiny, insoluble droplets floating in a solvent. Some sources say that colloids are by definition heterogeneous, but by the naked eye test, milk is a homogeneous liquid suspension of fats in water.
Most wines and liquors are homogeneous mixtures. The science of making wine and liquor is based on employing ethanol and/or water as a solvent on various substances - charred oak for bourbon whiskey, for example, or juniper in gin - to create unique flavors.
Water itself is an example of a homogeneous mixture. All but the purest water contains dissolved minerals and gases. These are dissolved throughout the water, so the mixture presents in the same phase and is homogeneous.
Many of the most common gaseous substances people encounter, including the most common one, air itself, are homogeneous mixtures.
The air that you breathe is a homogeneous mixture of oxygen, nitrogen, argon, and carbon dioxide, along with other elements in smaller amounts. Because each layer of the Earth's atmosphere has a different density, each layer of air is its own homogeneous mixture.
Natural gas is a gaseous heterogeneous mixture of methane and other hydrocarbons used as a fuel.
So-called "neon signs" actually use a number of different elemental gases and homogeneous gaseous mixtures to create their trademark glow. Argon and mercury vapor, for example, create a vibrant blue.
Nitrous oxide is one of many gaseous homogeneous mixtures used for anesthesia. As an anesthesia, nitrous oxide is used in a 50/50 solution with oxygen. In fact, doctors colloquially refer to nitrous oxide as "gas and air!"
Understanding homogeneous and heterogeneous mixtures is vital to building your knowledge of chemistry. Examples of homogeneous mixtures help reveal the remarkable scientific secrets that inform even the simplest parts of life. For more chemistry from us, check out Examples of Saturated Solutions, including carbonated water and salted butter. Happy learning!