Constrict
In chemistry, concentration (also known as thickening) means the removal of solvent from a solution . This increases the concentration of the dissolved substances. It is therefore the opposite of dilution .
The most commonly used methods rely on evaporation of the solvent. This can take place at normal ambient temperature, whereby the evaporation surface can be increased by placing the solution in open, flat vessels or by passing a gas stream through it. Another possibility is the so-called "blowing off" of the solution by means of a gas stream directed onto the surface of the solution. In this case, inert nitrogen is preferably used, since reactions with the solution must be avoided in order not to chemically change the substances contained. As long as the vapor pressure of the dissolved substances allows, evaporation can also be accelerated by increasing the temperature, in extreme cases by boiling the solution. The latter is also used as inputs or evaporation designated, this is understood in contrast to the actual concentration, the complete removal of the solvent to dryness. For more details see under evaporation.
A classic tool to concentration is the desiccator , a sealable and evacuable glass pot. A desiccant is placed in the bottom of the desiccator, which has a high affinity for the solvent and absorbs its vapor. The solution is placed in a bowl over a support grid and the desiccator is closed and, if necessary, pumped out.
A method that is more complex in terms of apparatus is narrowing in a rotary evaporator , in which the surface area is increased by rotating the solution with the vessel, the temperature can be set in a targeted manner using a water bath for the rotary vessel and the evaporated solvent is drawn off by negative pressure and distilled out through a cooler .
With these methods, concentration is only possible if the dissolved substance shows a significantly lower vapor pressure than the solvent . In the desiccator, a suitable selective absorbent can also help to concentrate solutions of volatile substances, although this is not loss-free.
A modern method is ultrafiltration and reverse osmosis on semipermeable membranes . The filter residue is narrowed here.
Individual evidence
- ↑ Manfred Hoffmann, Harald Gärtner: Chemistry, formulas, laws and technical terms . Compact Verlag, 2010, ISBN 978-3-8174-7892-7 , pp. 454 ( limited preview in Google Book search).
- ↑ Axel M. Gressner, Torsten Arndt: Springer Lexikon Chemie Medical Clinical Laboratory diagnosis of A to Z . Springer-Verlag, 2005, ISBN 978-3-540-23660-3 , pp. 360 ( limited preview in Google Book Search).
- ↑ Bruno P. Kremer, Horst Bannwarth: Introduction to Laboratory Practice, Basic Competencies for Laboratory Newbies . Springer-Verlag, 2014, ISBN 978-3-642-54334-0 ( limited preview in Google book search).
- ↑ Wolfgang Weichardt: Results of the Hygiene Bacteriology Immunity Research and Experimental Therapy Twenty-second volume . Springer-Verlag, 2013, ISBN 978-3-642-92389-0 , pp. 283 ( limited preview in Google Book search).