What is a homogeneous mix in chemistry

mixture

Schematic classification of the substances

Under a mixture (Mixture of substances) is a substance that consists of at least two basic substances.

Of a mixture One usually speaks of granular (heap, bulk material) or living components (seeds), which only mix with one another, but cannot mix homogeneously without dying off or becoming inoperable.

Physical chemistry

The raw materials are unchanged in the mixture. The starting materials are often unrecognizable because the mixture has different physical properties than any isolated starting material. However, when mixed, no new substance is created.

example: Concrete is a mixture of cement, concrete aggregate (sand and gravel) and water.

The specific properties such as density, boiling point or color depend on the mixing ratio (mass ratio) of the components.

  • In metallurgy, a molten mixture of different pure substances is ultimately also called alloy designated.
  • In another context one speaks of mixing or conglomerate.
  • Colloids are an intermediate form of homogeneous and heterogeneous mixtures. Solids are mixed in these liquids, but they occur in very small phases of a few molecules and therefore behave similarly to solutions (homogeneous).

If you want to separate mixtures into their pure substances, you use the different physical properties. This results in the selection of the respective separation method.

Homogeneous and heterogeneous mixtures according to their physical state

The different types of mixtures, which are differentiated according to the aggregate states of the mixed substances, can be divided into two groups:

  • Heterogeneous mixtures (Dispersions) are not completely mixed because the pure substances are in clearly defined phases, i.e. they are multiphase.
  • Homogeneous mixtures are pure substances mixed at the molecular level, i.e. single-phase

The following types of mixtures exist (red = homogeneous, yellow = heterogeneous):

mixture firmly liquid gaseous
in firm alloy, like bronzesponge, e.g. B. soaked bath sponge empty sponge, hard foam
mixture i.e.S., like granite
Heaplike gravel
in liquid solutionlike wine
suspensionlike mudemulsionlike milkfoam
in gaseous form Aerosol (Generic term) Gas mixture
Smoke, dust, like cigarette smoke Steam, fog

Types of Mixtures

Mixtures and blends can be differentiated according to the phase state in which they are present. If solid, liquid and gaseous are used as a basis, it turns out that in all areas relevant to human existence, mixtures and mixtures are far more important than pure substances.

Solid mixtures

Mixtures of solids can be of natural origin or of an artificial nature (created by humans). The naturally occurring mixtures that one encounters as local, regional or global components of the earth's surface seem easy to define. Examples of the diversity of such mixtures are lava, dolomite or granite. What is said about the formation is important, because it shows that all solids known to us have only become solids and that from a originally hot and gaseous phase in the course of their cooling from liquid to viscous and mushy to solids only in very long periods of geological history have changed. Example: Granite is a mixture or mixture of quartz, feldspar, mica and hornblende.

Liquid mixtures

Natural liquid mixtures are lavas or carbonated mineral springs. In the case of liquid mixtures, human influence has been demonstrable since historical times. Example: "Greek fire", presumably a mixture based on petroleum with pitch, sulfur and saltpeter[1], which was already used by Emperor Constantine I in the fourth century as a naval weapon. In a more modern form, one encounters a comparable mixture in the form of the Molotov cocktail, invented or rediscovered during World War II, a fire bottle filled with a mixture of gasoline and white phosphorus.

Gaseous mixtures

The best-known gaseous mixture is the air we breathe with proportions of oxygen, nitrogen, carbon dioxide and helium.

process technology

Macro blending and micromixing

In chemical reaction engineering, a distinction is made between the state of mixing of the reaction mass in a reactor:

  • Macro blending: that is all that one could 'see with the naked eye', the macro-mixing in the reactor is characterized by the residence time spectrum, which is e.g. B. can be obtained experimentally by 'tracer measurements'.
  • Micromixing: this is a characteristic of the fluid:
    • complete micromixing = molecularly disperse fluid (example: saline solution)
    • complete 'non-micromixing' = complete segregation = fluid with a dispersion of microscopically small closed fluid elements (example: milk / emulsion).

In English and also in some German schools the definition of the term is somewhat different: engl. macromixing and macrofluid = segregated fluid; micromixing and microfluid = molecularly disperse fluid. For the term 'macro mixing', as it was defined in the present case, 'contacting pattern' is then used.

Dimensions of mixtures

proportion of, concentration or salary is the material proportion of a substance in a mixture in terms of mass, volume or amount of substance:

Concrete examples:

Substance and mixture in legislation

Both terms occur in the legislation on hazardous substances and are defined somewhat differently from the diagram above: The legislator only uses "substance" for that which is declared in the scheme as "pure substance" (element or compound) and not as a generic term for everything. The term "mixture" (previously used by the legislator preparation Conversely, it is not a subset of material, but a parallel term. A different date applies to the introduction of the GHS for “substances” than for “mixtures”; that would not be possible with the definition given in the article.

literature

  • "Herder-Lexikon Geologie und Mineralogie", Verlag Herder KG, Freiburg im Breisgau 1972, ISBN 3-451-16452-3.

See also

  • Component, Mixing - on the legal issues of mixing
  • Mixed phase (thermodynamics) - a homogeneous phase, which consists of several substances
  • Mixture problems - a subgroup of mathematical problems

Web links

Individual evidence

  1. ^ Meyers Konversationslexikon, published in Bibliographisches Institut, Leipzig and Vienna, 5th edition from 1897, vol. 7