Mixture

In chemistry, a mixture is a substance made by combining two or more different materials with no chemical reaction occurring. The objects do not bond together in a mixture. A mixture can usually be separated back into its original components. Some examples of mixtures are: fruit salad, ocean water and soil. Mixtures are the product of a mechanical blending or mixing of chemical substances like elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. ^[1]

While there are no chemical changes in a mixture, physical properties of a mixture, such as its melting point, may differ from those of its components. Mixtures can usually be separated by any mechanical means. Mixtures are either homogeneous or heterogeneous.

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Homogeneous Mixtures

Main article: Homogeneity (physics)

Homogeneous mixtures are mixtures that have definite, consistent composition and properties. Particles are uniformly spread. For example, any amount of a given mixture has the same composition and properties. Examples are solutions and some alloys (but not all). A homogeneous mixture is a uniform mixture consisting of only one phase. Examples are gasoline and margarine.

Solutions

A solution is a homogeneous mixture of two or more substances (the solutes) dissolved in another substance (the solvent). Solutions have all particles within the size of atoms, small molecules or small ions, less than 1 nanometer (nm) in all dimensions ^[2] . A common example would be a solid dissolving into a liquid (i.e. salt or sugar dissolving in water or gold into mercury). Liquids dissolve into one another, and sometimes liquids dissolve into gases, for example water vapor and the atmosphere. Common examples include fountain drinks, where carbon dioxide is trapped in the liquid through carbonation. Several solution properties collectively called colligative properties change as a function of solute concentration. Solubility is a compound property.

Colloidal Dispersions

Main article: Colloid

Colloids are another type of homogeneous mixture in which the particles of one or more components have at least one dimension in the range of 1 to 1000nm, larger than those in a solution but smaller than those in a suspension. ^[2] In general, a colloid or colloidal dispersion is a substance with components of one or two phases. A colloid will not settle if left to sit. Jelly, milk, blood and glue are examples of colloid dispersions.

Heterogeneous Mixtures

Main article: Heterogeneous

Heterogeneous mixtures are mixtures with inconsistent, non-uniform composition. The parts of a heterogeneous composition can be mechanically separated from each other. Examples include salad, trail mix and granite.

Suspensions

Main article: Suspension (chemistry)

A heterogeneous mixture in which the particles, of at least one component is larger than 1μm (1000nm) in at least one dimension, larger than colloidal particles. ^[2] Unlike colloids, suspensions will eventually settle. An example of a suspension would be sand in water. Particles of suspensions exhibit the Tyndall effect, that is, they are big enough to disperse light, like colloids.

See also

• Colligative properties
• Molar solution
• Percentage solution
• Separation process
• Solubility equilibrium
• Suspension (chemistry)

References

1. ^ Atkins' Physical Chemistry, 7th Ed. by Julio De Paula, P.W. Atkins ISBN 0198792859
2. ^ ^{a b c} Chemistry: Matter and Its Changes, 4th Ed. by Brady, Senese, ISBN 0471215171