The words homogeneous and heterogeneous are often used in scientific contexts to describe kinds of mixtures, but they can be also used in other ways, such as to describe groups of people. But what do they actually mean, and what is the difference?
In this article, we’ll define homogeneous and heterogeneous, break down the differences between them, and provide some examples of the different things the words can describe, including both homogeneous and heterogeneous mixtures.
The word homogeneous generally describes things that are made up of parts or elements that are the same or very similar. The word heterogeneous is the opposite—it generally describes things that are made up of elements that are unalike. Scientifically speaking, a homogeneous mixture is one in which different parts (such as salt and water) have been uniformly combined into a new substance (salt water), while a heterogeneous mixture has parts that remain separate.
homogeneous vs. heterogeneous
Let’s start by looking at the beginnings of each word, which indicate how they differ. In homogeneous, homo- means “same.” In heterogeneous, hetero- means “different” or “other.”
In general use, the word homogeneous can describe something that is made up of parts or elements that are the same or very similar. It can also be used to describe two things as being the same or very similar in nature. For example, if a population of a nation is described as being homogeneous, it means that the people are all the same in some way, such as all having the same culture or ethnicity.
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By contrast, the word heterogeneous is used generally to describe something made up of different elements or parts, or to describe two things that are different from each other. A heterogeneous population of people consists of people that are different from each other in some way, such as having different cultures or ancestries.
The general use of these words is similar to the more specific scientific use.
homogeneous vs. heterogeneous mixtures
The words homogeneous and heterogeneous are most often used in scientific contexts, particularly in chemistry to describe mixtures.
Homogeneous mixtures are uniform in structure or composition. For example, if you mix table salt into water, this mixture is homogeneous because the salt completely dissolves into the water, meaning that the salt particles are evenly distributed throughout the water. Homogeneous mixtures are typically those whose component parts cannot be easily separated (such as in the example of the salt water mixture).
In contrast, heterogeneous mixtures consist of distinct substances and don’t have a uniform composition. As a simplified example, a salad is a heterogeneous mixture: you can see that a salad obviously consists of different, separate ingredients, such as lettuce, tomatoes, and carrots. If you scoop out some of the salad into a bowl, it may not have the same number of tomatoes as another scoop. The ingredients don’t blend together into a uniform whole but remain separate from each other and are unevenly distributed throughout the mixture.
Remember, the separate components of a homogeneous mixture come together to form a new substance, whereas the separate components of a heterogeneous mixture remain separate from each other.
In order to show how this works in practice, let’s look at some specific mixtures.
Is air homogeneous or heterogeneous?
Air is a homogeneous mixture. Air is composed of different gaseous elements, mostly oxygen and nitrogen. These atomic elements combine together to form air, which has a uniform composition: if you take a sample of air anywhere on Earth, it will always be made up of the same approximate percentage of oxygen, nitrogen, and other substances. Air is invisible to the eye and the different elements that make up air are not easily distinguished or separated from each other.
Is blood homogeneous or heterogeneous?
Blood is a heterogeneous mixture. Blood is made of a mixture of red blood cells, white blood cells, platelets, and plasma. Rather than mixing together, these four substances remain separate from each other in blood. Additionally, these four substances can be distinguished from each other in blood samples using microscopes and can be separated from each other using medical equipment.
Did you know antibodies are found in blood? Learn more about hoe antibodies work here.
Is concrete homogeneous or heterogeneous?
Concrete is a heterogeneous mixture. Concrete is made out of a mixture of water, cement, and aggregates such as gravel, sand, or chunks of rock. Concrete doesn’t have a uniform composition because the aggregates are spread randomly throughout it and remain as identifiable separate elements. The proportion of different stuff in concrete varies from one portion to another.
Is milk homogeneous or heterogeneous?
It can be argued whether milk is homogeneous or heterogeneous—the answer depends on which type of milk is being discussed. Whole milk that comes directly from a cow (or other animal) is a mixture that consists of globules of fat in water. It is possible to see these fat particles under a microscope, and looking at them shows that the fat globs are not uniformly distributed, which means that whole milk is a heterogeneous mixture. However, skim milk has all of these fat globs removed, and so it could be said to be a homogeneous mixture. Finally, many types of store-bought milk have been turned into a homogeneous mixture through homogenization, a process in which the fat globs are broken down and evenly distributed throughout the milk.
The terms heterogeneous and homogeneous refer to mixtures of materials in chemistry. The difference between heterogeneous and homogeneous mixtures is the degree to which the materials are mixed together and the uniformity of their composition.
A homogeneous mixture is a mixture in which the components that make up the mixture are uniformly distributed throughout the mixture. The composition of the mixture is the same throughout. There is only one phase of matter observed in a homogeneous mixture at a time. So, you wouldn't observe both a liquid and a gas or a liquid and a solid in a homogeneous mixture.
There are several examples of homogeneous mixtures encountered in everyday life:
- Air
- Sugar water
- Rainwater
- Vodka
- Vinegar
- Dishwashing detergent
- Steel
You can't pick out components of a homogeneous mixture or use simple mechanical means to separate them. You can't see individual chemicals or ingredients in this type of mixture. Only one phase of matter is present in a homogeneous mixture.
A heterogeneous mixture is a mixture in which the components of the mixture are not uniform or have localized regions with different properties. Different samples from the mixture are not identical to each other. There are always two or more phases in a heterogeneous mixture, where you can identify a region with properties that are distinct from those of another region, even if they are the same state of matter (e.g., liquid, solid).
Heterogeneous mixtures are more common than homogeneous mixtures. Examples include:
- Cereal in milk
- Vegetable soup
- Pizza
- Blood
- Gravel
- Ice in soda
- Salad dressing
- Mixed nuts
- Bowl of colored candies
- Soil
Usually, it's possible to physically separate components of a heterogeneous mixture. For example, you can centrifuge (spin out) solid blood cells to separate them from the plasma of blood. You can remove ice cubes from soda. You can separate candies according to color.
Mostly, the difference between the two types of mixtures is a matter of scale. If you look closely at sand from a beach, you can see the different components, including shells, coral, sand, and organic matter. It's a heterogeneous mixture. If, however, you view a large volume of sand from a distance, it's impossible to discern the different types of particles. The mixture is homogeneous. This can seem confusing!
To identify the nature of a mixture, consider its sample size. If you can see more than one phase of matter or different regions in the sample, it is heterogeneous. If the composition of the mixture appears uniform no matter where you sample it, the mixture is homogeneous.