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Explanation of the Types of Mixtures by Ron Kurtus - Succeed in Chemistry. Key words: suspension, colloidal, solution, solvent, solute, molecules, particles, elements, ions, homogeneous, homogenized, separation, water, oil, vinegar, whipped cream, evaporation, distillation, School for Champions. Copyright © Restrictions

Types of Mixtures

by Ron Kurtus (15 September 2005)

A mixture is the blending of two or more dissimilar substances that do not chemically combine to form compounds and that can typically be separated by non-chemical means. Mixtures can be classified into three types: suspension mixture, colloidal mixture or solution, according to how they combine and can be separated.

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Suspension mixture

A suspension mixture is usually created by stirring together two or more ingredients, where the particles are typically large enough to be seen by the unaided eye or a magnifying glass. The ingredients of a suspension mixture are heterogeneous, meaning that they are not evening distributed throughout. Most mixtures are suspension mixtures.

Solid-solid mix

Many suspension mixtures consist of solids mixed with solids. Cake mix is an example of visible solid particles mixed together by a means of stirring. Dirt or soil is another example of a solid-solid suspension mixture.

These mixtures can be separated by sifting. Sometimes shaking will cause the heavier particles to settle to the bottom.

Solid-fluid mix

If solid particles are mixed in a liquid or gas to form a suspension mixture, the ingredients will soon separate, with the heavier solid particles settling at the bottom. For example, if you mixed sand and water, the sand would soon sink to the bottom.

If the solid particles are lighter than the liquid--as in the case of sawdust mixed in water--they will separate and float to the top.

A major part of air pollution consists of smoke and dust particles mixed within the atmosphere. This is a suspension mixture. After a while, the these solid particles will settle to the ground.

Besides settling, filtration can also be used to separate the ingredients.

Fluid-fluid mix

If visible globules of a liquid are mixed in a liquid or gas solvent, the ingredients will soon separate. If the globules are heavier, they will settle at the bottom. If the globules are lighter, they will float to the top.

Colloidal mixture

A colloidal mixture is a homogeneous combination of solid or liquid particles mixed within a liquid or gas solvent.

(Note: The material you add is called the solute and the material you are adding to is called the solvent.)

Size of particles

The size of solute particles in a colloidal mixture are much smaller than the particles in a suspension, but they are not as small as those in a solution. The particles in a colloidal mixture are typically as small as a clump of molecules that may not even be visible with a common microscope.

What makes a colloidal mixture unusual is that the solute particles do not break down any further to be single molecules--thus forming a solution. Instead, "something" coats the particles and prevents them from completely dissolving in the solvent.

Blending

The blending of materials in a a colloidal mixture is usually more aggressive than the simple stirring done in a suspension. Often the material is violently mixed or shaken. A good example is the paint-mixer machine that actively shakes the can to thoroughly mix the paint materials to minimize settling.

Some examples of colloidal mixtures are mayonnaise, Jell-O, fog, butter and whipped cream.

Solution

A solution is a homogeneous mixture where one substance is dissolved in another substance. The solute dissolves in the solvent. The solvent is a liquid or gas, and the solute can be a solid, liquid or gas.

Dissolving

Dissolving means that after the solute is put in the solvent, it breaks to an atomic, ionic or molecular level and can no longer be seen as a separate entity. For example, mixing the solid material salt into the liquid water results in the salt dissolving into water and creating the salt water solution. The salt breaks into Sodium (Na+) and Chlorine (Cl-) ions within the water solvent.

Polar or non-polar

Typically, all the molecules in a solution are either polar or non-polar. For example, Nitrogen (N2), Oxygen (O2) and Carbon Dioxide (CO2) are all non-polar molecules. They mix well together to form the solution we call air.

Under normal conditions combinations of polar and non-polar molecules do not mix to form a solution. There are exceptions, such as the non-polar Carbon Dioxide dissolving in the polar solvent water (H2O) under high pressure.

Separation

The solute and solvent in a solution cannot be separated unless one of the ingredients changes state of matter. For example, by heating the solution, one material may evaporate. This is also called distillation.

(For more information, see Chemical Solutions and Polar and Non-Polar Molecules.)

Summary

Mixtures can be classified into three types: suspension mixture, colloidal mixture or solution, according to how they combine and can be separated. Suspension mixtures have larger solute particles, colloidal mixtures have much smaller particles, and particles in a solutions completely dissolve into the solvent.


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