Types of Mixtures

Two Types of Mixtures in Chemistry

There are two types of mixtures. These are:

1. Homogeneous mixture
2. 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

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.

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.

Types of Mixtures: Heterogeneous Mixtures

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:

1. Colloid.
2. 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
  • Ex: Oil in water
• Foam: Gas particles in liquid/solid
  • Ex: Soap bubbles
• Aerosol: liquid/solid particles in a gas
  • Ex: Smoke: soot in carbon dioxide

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.

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.

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.

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.