Mixture, Chemical
Despite their presence in all fields of chemistry, chemical mixtures cannot be represented by any formula. This is because they contain two or more distinct chemical components that are either heterogeneous or homogeneous. The substances in a mixture, no matter how closely they have intermingled, have no firm chemical interaction or bonding between or among themselves.
A heterogeneous mixture combines substances which have distinct and different phases, such as ice cubes and water. In homogenous mixtures, the atoms or molecules of the ingredients are interspersed with each other to form a single phase, as in a mixture of gases.
There are four types of mixtures which are either heterogeneous or homogeneous. The first type of mixture is called a "solution," in which chemical components (whether gas, solid, or liquid) combine to form a single-phase, homogeneous mixture whose components are evenly distributed. An "azeotropic" mixture is one in which at least two liquids combine to make a solution whose composition remains the same upon distillation. A "colloid" is a mixture whose components dissolve spontaneously into a solvent; they have the unusual property of not being able to pass through a membrane because they contain small, solid particles (the colloid, or dispersed phase) thoroughly mixed into a liquid (dispersion medium). The fourth type of mixture is a "suspension". A suspension consists of two or more substances formed into a mixture that appears at first to be homogeneous. However, after a period of time, the mixture becomes heterogeneous. An example of a suspension is cough syrup.
A mixture's parts may or may not be dispersed evenly, but its components can usually be separated from each other, at least theoretically, through physical means (distillation, crystallization, etc.). They retain their own chemical characteristics despite being mixed together. This is in contrast to chemical compounds, whose components react with one other and thus cannot easily be taken back apart.
One minor exception to this rule can occur when the components of a mixture have attractive or repulsive forces that act upon each other. In this case, the reaction among the components may affect the properties of the overall mixture. For instance, the total volume of several liquids all mixed together might actually be greater than the sum of all the liquids' individual volumes before they were mixed together.
Chemical mixtures can be both natural and artificial. Some examples of natural mixtures, chemically speaking, are wood, blood, vegetable oils, milk, petroleum, air, marble, latex, and ocean water. Artificial mixtures include alloys, cement, glass, perfumes, paint, and some plastics.
When dealing with chemical mixtures in the laboratory, scientists and researchers will sometimes use a mathematical technique known as "alligation." This is a formula used to figure out the proper proportions of chemicals to put into the mixture. It can also calculate the value of a certain property of a mixture by determining the values of that property in its respective component. Alligation works because the ingredients in a mixture retain their unique chemical characteristics.
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