Definitions

mixture

mixture

[miks-cher]
mixture, in chemistry, a physical combination of two or more pure substances (i.e., elements or compounds). A mixture is distinguished from a compound, which is formed by the chemical combination of two or more pure substances in a fixed, definite proportion. The components of a mixture retain their own chemical properties and may be present in any proportion. For example, iron filings may be mixed with powdered sulfur in any proportion, and even if very fine iron powder is carefully mixed with powdered sulfur, the two components are easily separated by means of a magnet; the magnet will draw out the iron from the mixture. However, if seven parts by weight of iron filings or powder are mixed with four parts by weight of powdered sulfur and the mixture is heated to a red glow (e.g., in a test tube, using a Bunsen burner), the iron and sulfur react to form the compound iron sulfide; they are chemically combined and are not readily separated. The iron sulfide is not attracted by a magnet. Mixtures are often classified as homogeneous or heterogeneous. Solutions and colloids are homogeneous mixtures. The components of a homogeneous mixture are too intimately combined to be distinguished from one another by visual observation. A suspension is a heterogeneous mixture. The particles in a heterogeneous mixture are coarse enough to be distinguished by visual observation. Alloys are mixtures of metals and may be either homogeneous or heterogeneous. The components of a mixture usually can be separated by physical means such as distillation, evaporation, precipitation, filtration, solvent extraction, or chromatography.

In chemistry, a mixture is a substance made by combining two or more different materials without a chemical reaction occurring (the objects do not bond together).

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

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.

Homogeneous mixtures

Homogeneous mixtures are mixtures that have definite, consistent 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 when a Homogeneous mixture of one 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. 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.

Heterogeneous mixtures

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, sand, salt mixed with sand, sandy water, ocean water, and soil.

Suspensions

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. Unlike colloids, suspensions will eventually settle. An example of a suspension would be sand in water another example would be clothing made up of 2 or more materials such as cotton and polyester. Particles of suspensions exhibit the Tyndall effect, that is, they are big enough to disperse light.

Colloidal dispersions

Colloids are heterogeneous mixtures 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. In general, a colloid or colloidal dispersion is a substance with components of one or two phases. It creates the Tyndall effect when light passes through it. A colloid will not settle. Jelly, milk, blood, paint, fog, and glue are examples of colloid dispersions.

Mixtures and compounds

A compound is not a mixture. A compound has very different properties than the elements it is made of, but a mixture contains several substances which keep their properties.

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