Chemical working processes

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Chemical work processes are methods and techniques that are used in the chemistry laboratory to carry out subject-specific tasks. Special devices are used for this. Typical tasks in the laboratory are:

  • Production of new substances ( synthesis , preparations )
  • Separation of a substance mixture (substance separation) or purification of a substance
  • Qualitative and quantitative evidence of substances or amounts of substances in a sample ( analysis , identification of a substance in a sample)
  • Clarification of the molecular or crystalline structure of a material (structural analysis, crystallography)
  • Measurement of a substance-specific property or its change in the course of a chemical reaction (e.g. by heating, distillation, extraction, chromatography)

In many cases, a separate laboratory jargon has become established for these activities .

Heating and cooling

Many processes in the chemical laboratory (for example: carrying out reactions, separation processes) require the supply of thermal energy or the setting of a certain temperature. The work processes and resources required for this are:

  • Burners such as Bunsen burners or Teclub burners etc.
  • Heating baths - are mainly needed to achieve constant temperatures. Depending on which temperature is required, different transmission media are used:
  • Cold mixtures
  • Liquid nitrogen - above all to liquefy substances with low boiling temperatures.

The targeted mixing of substances such. B. to produce a solution of a certain concentration (diluting, concentrating) is an important activity in the chemistry laboratory, which requires chemical computation ( stoichiometry ) as well as the use of volume measuring devices and scales. The separation of mixtures of substances into pure substances , e.g. B. for cleaning a raw preparation, takes place via a material separation process. Are these used to remove educts, by-products and the like? similar to separate “impurities” from a desired product , these processes are called cleaning processes. B. drying as the removal of moisture (water) from a preparation . The main working methods in this area are:

  • Distillation - classic separation method, the principle of which is based on the utilization of different boiling temperatures of the components.
  • Steam distillation - special variant that enables gentle separation. Often used for natural substances .
  • Filtering - there are different types of filters.
  • Recrystallization - is used to clean substances.
  • Chromatography - is used to analyze mixtures of substances based on the physical or chemical properties of their components. There are different variants:
    • Thin-layer chromatography : the sample is dropped onto a plate coated with silica gel and this is placed in an eluent. The eluent is sucked through the silica gel from bottom to top and the sample is separated.
    • Gas chromatography : the sample is forced through a capillary by a carrier gas (usually hydrogen), whereby the various components are separated.
    • HPLC (HighPressureLiquidChormatography - high performance liquid chromatography): The sample is pumped into a column under high pressure (approx. 100 bar), whereby the above-mentioned principle is applied again.
  • When shaking out , a solute is extracted by another solvent .

Measurement method

  • Mass determination with the analytical balance
  • Volume determination with:
  • pH value measurement using a pH meter or an acid-base titration with indicator or pH electrode
  • Method of instrumental analysis to determine the concentration, molar mass, density, optical activity, viscosity and similar substance-specific constants via:
    • optical methods,
    • spectroscopic methods,
    • chromatographic methods,
    • electroanalytical and other physical methods.

These include B. photometric measurements and the determination of the refractive index ( refractometry ).

For further examples see under instrumental analysis , quantitative analysis , viscometry, osmometry , polarimetry .

Wet chemical analysis methods such as volumetry (titration, dimensional analysis) and gravimetry (precipitation analysis ) are not included in the instrumental analysis methods.

Temperature measurement, phase change temperature measurements and determinations of molar mass

Mainly necessary to determine the properties of a substance, but also to maintain the optimal temperature for a chemical reaction.

Detection procedure with the help of chemical reactions

  • Cation separation process - a process in which components can be separated and identified in a predetermined order. However, only positively charged particles (positively charged ions = cations) are separated
  • Detection reactions for anions (negatively charged particles) - certain reagents (detection agents) lead to special reactions in the presence of certain particles (analytes) (see under cation detection , anion detection , detection reaction ).
  • Detection reactions for special groups of organic substances
  • Preliminary samples , e.g. B. the borax pearl

Craft work

Automated work processes

In the course of the rationalization of work processes, laboratory work that was previously carried out manually is also increasingly being automated. For this purpose, laboratory automation systems are used that record measured values ​​(temperature, pressure, pH value , etc.) with the help of suitable sensors and control the laboratory devices (heating / cooling systems, laboratory stirrers , pumps, etc.). In this context, the working procedures are referred to as basic procedural operations . See also laboratory automation .

Web links

Individual evidence

  1. ↑ Michael Wächter: Chemielabor - Introduction to Laboratory Practice , Wiley-VCH, 1st edition, 2011, pp. 343–359, ISBN 978-3527329960 .
  2. ↑ a b Michael Wächter: Chemielabor - Introduction to Laboratory Practice , Wiley-VCH, 1st edition, 2011, pp. 60-102, ISBN 978-3527329960 .
  3. ↑ Michael Wächter: Chemielabor - Introduction to Laboratory Practice , Wiley-VCH, 1st edition, 2011, pp. 27-35, ISBN 978-3527329960 .
  4. ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 173-187, ISBN 3-211-81116-8 .
  5. ^ Herbert Feltkamp, ​​Peter Fuchs, Heinz Sucker (editors): Pharmaceutical Quality Control , Georg Thieme Verlag, 1983, p. 345, ISBN 3-13-611501-5 .
  6. ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 104–123, ISBN 3-211-81116-8 .
  7. ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 214-218, ISBN 3-211-81116-8 .
  8. ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 200-214, ISBN 3-211-81116-8 .
  9. ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 193–194, ISBN 3-211-81116-8 .
  10. ^ Walter Wittenberger: Chemische Laboratoriumstechnik , Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 84–89, ISBN 3-211-81116-8 .
  11. ^ Herbert Feltkamp, ​​Peter Fuchs, Heinz Sucker (editors): Pharmaceutical Quality Control , Georg Thieme Verlag, 1983, pp. 248–249, ISBN 3-13-611501-5 .
  12. ^ Herbert Feltkamp, ​​Peter Fuchs, Heinz Sucker (editors): Pharmaceutical Quality Control , Georg Thieme Verlag, 1983, p. 299, ISBN 3-13-611501-5 .