A mixture is a material containing two or more elements or compounds that are in close contact and are mixed in any proportion. The components of a mixture can be separated by physical means.
For example, air, gun powder, etc.
Mixtures combine physically in no spesific proportions. They just mix!
Note that a mixture:
- consists of two or more different elements and/or compounds physically intermingled,
- can be separated into its components by physical means, and
- often retains many of the properties of its components.
Properties of a mixture :
Within the mixture, it can be classified into two main categories: homogeneous and heterogeneous:
- A homogeneous mixture is one in which the compositions of its constituents are uniformly mixed throughout. Homogeneous solutions may also be called a solution, because it consists of solubility, where a solute dissolves completely in a solvent.
Usually the solvent is a liquid, however the solute can be either a liquid, solid, or a gas. In a homogeneous solution, the particles are spread evenly amongs the solvent, therefore, the particles cannot be separated from the solvent. For instance, if salt and water are mixed together, it is nearly impossible to separate the salt from the water, even with filtration, because the solute is mixed so well with the solvents.
A few more examples of homogeneous mixtures include sugar water, which is the mixture of sucrose and water, and gasoline, which is a mixture of dozens of compounds.
Examples of Homogeneous Mixtures
Seawater is solution of the compounds of water, salt (sodium chloride), and other compounds.
- A heterogeneous mixture is a nonuniform mixture in which the components separate and the composition varies. Unlike the homogeneous mixture, heterogeneous mixtures can be separated through physical processes.
An example of a physical process used is filtration, which can easilty separate the sand from the water by using a filter basket. Some more examples of heterogeneous mixtures include salad dressing, rocks, and oil and water. Heterogeneous mixtures are also called suspension mixtures and separate if they are left standing long enough. Consider the idea of mixing oil and water together. It does not matter the amount of time it takes to shake this because when it settles, the oil will always be separated from the water due to the difference in its density.
Examples of Heterogeneous Mixtures
Mixtures that fall between a true solution and a heterogeneous mixture are called colloidal mixtures. A mixture is considered colloidal if one or more of its dimensions of length, width, or thickness is in the range of 1-1000 nm. A colloidal mixture can be determined by passing a beam of light through the mixture. In this situation, the light is scattered and can be seen by the viewer. This is know as the Tyndall effect. In contrast, if the beam of light was passed through a true solution, the observer would see no light when standing perpendicular to the mixture.
Solutions: molecules ~0.1-2 nm in size
Colloids: molecules ~ 2-1000 nm in size
Suspensions: molecules greater than ~ 1000 nm in size
Example of Colloidal Mixtures
milk is a colloid of liquid butterfat globules dissolved in water.
MIXTURES can be separated in different ways:
- A mixture of two liquids can be separated by DISTILLATION
- A mixture of a liquid and an INSOLUBLE solid can be separated by FILTERING
- A solid can be separated from a solution by evaporating off the liquid. for example with REKRISTALIZATION and SUBLIMATION.
- A mixture of dyes can be separated using CHROMATOGRAPHY. The mixture is placed onto chromatography paper and water is used to separate the dyes.