When you take a breath of fresh air, you aren't just breathing in oxygen. You are actually inhaling several gases, such as nitrogen and hydrogen. You can't actually see the different components, are they are blended together in a uniform mixture.
Air isn't the only mixture we see in our daily lives, from the soap we use to wash our hands, to the blood pumping in our veins, and to the soil that feeds our plants. All around us, there are mixtures, and in this article, we will be learning all about them!
- This article is about types of mixtures.
- First, we will define a mixture.
- Then, we will look at homogeneous mixtures and their two special types: solutions and alloys.
- Next, we will look at heterogeneous mixtures and their two special types: colloids and suspensions.
- Then we will use our new skills to identify the type of mixture.
- Lastly, we will learn about some different methods of separating mixtures.
Two Types of Mixtures in Chemistry
A mixture is a substance that is formed by combining two or more other substances. This process is a physical, not chemical change, so each component retains its original properties.
There are two types of mixtures. These are:
- Homogeneous mixture
- Heterogeneous mixture
The main difference between these two types is the distribution of the components within the mixture.
Mixtures are different from compounds since compounds are formed chemically, while mixtures are formed physically. Also, mixtures can be made from both compounds and elements, while compounds can only be made from elements.
Types of Mixtures: Homogeneous Mixtures
A homogeneous mixture is a mixture with a uniform composition (i.e. it only has one phase).
A phase is a portion of a sample that has a uniform composition and characteristics
One key point about homogeneous mixtures is that you can't tell where one part ends and another begins. A good example of this is saltwater. In a sample of saltwater, you cannot see the individual grains of salts that have been dissolved, you instead see a unified cloudy mixture.
Another key point is that homogeneous mixtures have a uniform distribution, but not a set ratio, like in a compound. For example, in the compound NaCl, there is always 1 mole of Na per 1 mole of Cl. However, in the mixture of saltwater, there could be 3 mols of salt per 10 mol of water or 6 mols of salt per 12 mols of water. The ratio doesn't matter, as long as the dissolved salt ions are spread evenly.
The mixture of salt water is a solution.
A solution is a homogeneous mixture that is formed when a solute is dissolved in a solvent.
Here is what that would look like in a solution:
Fig.1-Different homogeneous salt water mixtures
The salt ions are spread evenly. If you cut either sample in half, the distribution is the same. This is why these solutions are considered "uniform".
One special type of homogeneous mixture is an alloy.
An alloy is a homogeneous mixture of a metal + another metal or nonmetal
Types of Mixtures: Heterogeneous Mixtures
In a heterogeneous mixture, the composition is not uniform and there are clear and distinct phases.
Oil and water do not mix. If you pour oil into a glass of water, the oil will float above it. Each of these is a clear phase, and we can easily tell them apart. All mixtures of immiscible (don't mix) liquids are heterogeneous.
Heterogeneous particles are not distributed evenly, as shown below.
Fig.2-Different heterogeneous mixtures.
The mixture of oil and water would look like the example on the right. If I cut both of these samples into several pieces, each piece would have a different composition, which is why they are heterogeneous.
There are two special types of heterogeneous mixtures:
- Colloid.
- Suspension.
Colloids are a mixture where small, insoluble particles are suspended in another substance. Depending on the state of the suspended particles and the substance they are suspended in, colloids can have different names:
- Sol: Solid particles in a liquid
- Ex: Paints: pigment particles in water
- Emulsion: Liquid particles in a liquid
- Foam: Gas particles in liquid/solid
- Aerosol: liquid/solid particles in a gas
- Ex: Smoke: soot in carbon dioxide
Suspensions are a mixture where large, insoluble particles are suspended in another substance, but will eventually settle.
An example of a suspension is flour in water. When it is initially stirred, the flour particles are suspended in the water. However, after some time passes, the flour will sink to the bottom.
While colloids and suspensions may be similar to solutions, they are different. There are two main differences. The first is that colloids/suspensions have two phases, since the particles are insoluble, while solutions only have one phase since the particles are soluble.
The second difference is the size of the particles, as shown below.
Fig.3-Different sizes of particles for different mixture types
The particles in a solution are individual molecules/ions, while they are much larger in colloids and suspensions.
The size of these particles also affects how light interacts with them, called the Tyndall effect.
When light passes through a colloid/suspension, the particles deflect the light, causing it to scatter. This is called the Tyndall effect.
Here is what that looks like:
Fig.4-The Tyndall effect.
Essentially, the light particles (photons) are bouncing off the particles in the colloid/suspension, so they are visible. However, the particles in a solution are not large enough to cause this effect, so the light isn't visible.
Types of mixtures and their examples
Now that we have a good understanding of the different types of mixtures, let's try identifying them.
What type of mixture are the following examples? a) air b) chocolate chip cookie c) sand in water d) bronze e) muddy water f) mud
a) Air is a homogeneous mixture since it has a uniform composition, and you cannot distinguish the individual parts (nitrogen, oxygen, etc.)
b) A chocolate chip cookie has two phases: The chocolate chips and the cookie. Since it has two distinct phases, it is a heterogeneous mixture.
c) Sand cannot be dissolved in water. When it is initially mixed in, it will be suspended in the water, but will eventually settle. Because of this, it is a suspension/heterogeneous mixture.
d) Bronze is a mixture of two metals: copper and ion. Since it only has one clear phase, it is an alloy/homogeneous mixture
e) Muddy water is a mixture of water and mud. Since the mud doesn't dissolve in the water and its particles are large/will settle, it is a suspension/heterogeneous mixture.
f) Mud is a mixture of compounds like silt, clay, or soil mixed in water. These compounds are not soluble in water and are instead in suspension, however, they will not settle. Because of this, it is a colloid/heterogeneous mixture.
Separation of mixtures
Since mixtures are the result of a physical combination, they can be separated through non-chemical (physical) means.
Below is a table listing some common separation methods and when they can be used.
| Name of Method | Process | Used to separate |
| Filtration | A filter paper is placed in a funnel, and the mixture is poured over it. The solid particles will be caught by the filter, while the liquid will pass through | Liquids from insoluble solid |
| Evaporation | The mixture is heated, so the liquid is boiled off | Soluble solids from a liquid |
| Distillation | The mixture is boiled and then condensed. The different components will evaporate at different temperatures | Two or more liquids that are miscible/mixable with different boiling points |
| Chromatography | The solution is spotted onto a silica gel plate, which is placed in a solvent. The solvent will carry the different components at different rates, separating them | Compounds with similar properties, but different polarities. |
| Separation funnel | The mixture is placed in a separation funnel, which is shaken/inverted several times until the liquids separate | Immiscible liquids (have different densities) |
Depending on the mixture, multiple methods can be used. For example, a mixture of sand and water can be separated through evaporation or filtration, but filtration is often easier/faster.
Types of Mixtures - Key takeaways
- A mixture is a substance that is formed by combining two or more other substances. This process is a physical, not chemical change, so each component retains its original properties.
- A homogeneous mixture is a mixture with a uniform composition (i.e. it only has one phase)
- A phase is a portion of a sample that has a uniform composition and characteristics
- A solution is a homogeneous mixture that is formed when a solute is dissolved in a solvent.
- An alloy is a homogeneous mixture of a metal + another metal or nonmetal
- In a heterogeneous mixture, the composition is not uniform and there are clear and distinct phases.
- Colloids are a mixture where small, insoluble particles are suspended in another substance.
Suspensions are a mixture where large, insoluble particles are suspended in another substance, but will eventually settle
When light passes through a colloid/suspension, the particles deflect the light, causing it to scatter. This is called the Tyndall effect
There are several ways to separate mixtures such as filtration, evaporation, distillation, chromatography, and separation using a separation funnel
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