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Mixture

Definition

According to the OSHA Hazard Communication Standard, 29 CFR 1910.1200, a mixture is "any combination of two or more chemicals if the combination is not, in whole or in part, the result of a chemical reaction."

A chemist defines a mixture as a combination of two or more substances in which each substance retains its own chemical identity and properties.

In general, mixtures have no fixed composition. The amount of one or more components (substances) can usually vary over a wide range.

Additional Info

Mixtures generally fall into one of two categories:

A homogeneous mixture has uniform chemical composition, appearance and properties throughout. A simple example is air, which is a homogeneous mixture of gases consisting primarily of nitrogen and oxygen. Another example would be dissolving a small amount of sugar in a glass of water. After stirring, every section of the aqueous solution would be identical in composition, appearance and physical properties (such as boiling point, for example). A heterogenous mixture has different compositions, appearance and properties at various points in the mixture. A simple example is a chocolate chip cookie; at some points we encounter a chocolate chip and at others we encounter cookie dough. Another example is a mixture of ice and water; at one point we might encounter a solid, but at another we might have a liquid.

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An important property of mixtures is that they can (usually) be separated into their individual components without requiring any chemical reactions. For example, we can evaporate our sugar-water solution to obtain pure water or pure sugar. Likewise, we could put our chocolate chip cookie into water to dissolve away the dough and collect pure chocolate chips.

A microscopic view

When chemicals are combined, they can either form a mixture or they can chemically react to form new chemical species. For example, consider atoms A (blue) and B (red). If they do not react chemically, we obtain a mixture:



If each atom of A reacts with exactly one atom of B, we can form a new molecule AB that contains one atom of A chemically bonded to one atom of B. This is a chemical reaction because the new material will have different physical and chemical properties than either A or B.



Sometimes, we might form AB but have some A and/or B left over (the reaction might be reversible, or we may have put in more of one component). In these cases, one or more of the starting materials (A and/or B) as well as the new chemical species (AB) will be present in our resulting mixture. This is sometimes called an incomplete reaction:



MSDS Relevance OSHA Hazard Communication Standard, 29 CFR 1910.1200, mentions mixtures in some very specific ways. For example: If one combines two chemicals that do not interact when combined, then the mixture can be assumed to have the same properties and hazards as the individual components. Creating a new MSDS in this case is very easy. If the process of mixing causes a chemical change (reaction; production of new chemical species) to any significant degree, then the physical properties and hazards of the resulting mixture must be assessed. Creating an MSDS in this case would require a search of the scientific literature and/or possibly laboratory testing. Further Reading The following OSHA interpretations may be useful: Definition of a mixture under the Hazard Communication standard. Interpretation of the Hazard Communication standard as it applies to mixtures. One MSDS may apply to multiple complex mixtures having similar hazards. Requirements for providing MSDS information for carcinogens which are a residue in a mixture. Separating Mixtures and Classifying Matter quiz at General Chemistry Online! Fact Monster's entry on mixtures. Review and Practice on Classification of Matter at TeacherBridge. Elements, Compounds and Mixtures at TutorVista.com

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See also: chemical formula, mole and molecular weight.

Additional definitions from Google and OneLook.

Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.