Types of Mixtures

Mixtures

Iced tea is refreshing on a hot summer day. Iced tea is not an element, as it is composed of more than one substance. This makes iced tea a compound, composed of tea, water, and sugar. Sometimes, compounds like iced tea are called mixtures.

A mixture is a combination of two or more substances that are not chemically united and do not exist in fixed proportions to each other. A pure substance, on the other hand, has a constant composition with a very exact ratio of elements. Most natural substances are mixtures. In fact, it is difficult to find an absolutely pure substance. Sometimes, it is easy to determine whether a material is a mixture or not. Other times, it is quite hard, because the individual particles are quite difficult to see. According to kinetic molecular theory, all particles are in constant, random motion. Sometimes, the attraction between particles is enough that they will join together into a particle that is large enough to see. Mixtures which have a composition that is not uniform are called heterogeneous mixtures. The prefix hetero- means “different”. This means that heterogeneous mixtures have different parts. Mixtures that have a composition which is uniform are called homogeneous mixtures. The prefix homo- means “sameness”. This means that homogeneous mixtures are the same throughout.

All of the components of a mixture keep their own physical properties when they combine. Examples of physical properties include boiling point, ability to dissolve, and particle size. When components of mixtures vary in physical properties, processes such as boiling, dissolving, or filtering are used to separate the mixture. Other mixtures can be separated by the process of filtering or decanting. These processes take place when the particles in the mixture are small.

Look at the image to the left. The water in the lake is a solution of salt and water. As the water evaporates, the salt is left behind or deposited. Salt has a much higher boiling point when compared to water. This means that the salt will not evaporate.

 

Particle Size

You know that mixtures can be heterogeneous or homogeneous, but did you know that they can be further classified? According to their particle sizes, mixtures can be divided into three groups: solutions, colloids, and suspensions. In this interactivity, click on each of the folder "tabs" to learn more about mixtures and their associated particle sizes.

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The Tyndall Effect

Particles in suspensions are visual to the naked eye, but particles in a colloid and a solution are not. The particles in a solution are so small that they do not even reflect a beam of light. The particles in a colloid reflect light. This scattering of light in a mixture is called the Tyndall Effect. You may have seen a “stream” of light coming through a window in your house; this is an example of the Tyndall Effect. The particles of dust in the air are scattering the light of the sunshine coming through the window. The table below is a summary of the similarities and differences between suspensions, colloids, and solutions

	Solution	Colloid	Suspension
Type of Mixture	Homogeneous	Homogeneous	Heterogeneous
Particle Size	Smaller than 1 nm	1nm-1µm	Larger than 1µm
Displays the Tyndall Effect	No	Yes	Yes
Separated by Decanting or Filtering	No	Yes	Yes

Solutions

A solution is a mixture of two or more substances. Since solutions are uniform they are homogeneous mixtures. These mixtures are composed of two parts; the solute and solvent. Did you know that not all solutes will dissolve? There are factors that affect the solubility of a solution. View this presentation to learn more about solutions, solubility, and the factors that affect solubility.

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Analyzing a Solubility Curve Review

Now that you have learned how to analyze a solubility curve, complete this non-graded activity to check your knowledge. In this activity, read each statement and decide whether it is True or False. Then, click SUBMIT to check your response. Click on the interactivity thumbnail, and then click NEXT to get started.