Carbon dioxide
carbon dioxide (usually carbon dioxide called) is belonged a chemical compound made of carbon and oxygen and thereby beside carbon monoxide to the group of the carbon oxides. Its chemical formula is CO 2.
Carbon dioxide is color and odorless gas. It is with a concentration of approx. 0.04% (at present 378 ppm) a natural component of air and develop with the burn of carbon-containing substances, if sufficient oxygen is present (with lack Carbon monoxide develops). Also in the organism of organisms carbon dioxide develops as dome product of the Zellatmung. The CO 2 is delivered thereby over the breath. Turned around plants, some bacteria and Archaeen in the situation to convert CO 2 by the carbon dioxide adjustment into biomass. Thus plants produce for example with photosynthesis from inorganic CO 2 glucose.
| Structural formula | |
|---|---|
| |
| general | |
| name | carbon dioxide |
| other names | carbon dioxide, carbon (IV) - oxide |
| sum formula | CO 2 |
| CAS number | 124-38-9 |
| short description | colorless, odorless gas |
| characteristics | |
| mol mass | 44.0099 g mol |
| state of aggregation | gaseously |
| density | 1.98 kg/m ³ |
| melting point (Tripelpunkt) | -56.6 °C (at 5,81 bar) |
| point of sublimation | -78.5 °C |
| steam pressure | 57.3 bar (20 °C) |
| of solubility in water (pure CO 2, 1 bar) | 1.6 g/l (20°C)
3,2g/l with 0°C |
| solubility in water (from air, 1 bar) | 0.5 mg/l (20°C)
1.0 mg/l (0°C) |
| critical temperature | 31 °C |
| critical pressure | 74.0 bar |
| of thermal capacity C p | 0.83 kJ/(kg K) |
| heat conductivity | 0.01457 w (m·K) |
| Speed of sound | 258 m/s |
| of safety references | |
| R and S-sentences |
of R: - |
| MAK | 5000 ppm |
| as far as possible and common, are used SI-UNITs. If not differently notes, the indicated data apply with standard conditions. | |
To table of contents |
representation
technical
technical wins one carbon dioxide by burning coke with surplus air or as by-product when lime burning and following cleaning (z. B. Bind to potassium carbonate to hydrogencarbonate and following setting free by heating up).
Also natural Gasquellen (minerals water) are used for production.
in the laboratory yardstick
release from carbonates (z. B. Calcium carbonate) by acids (z. B. Hydrochloric acid).
physical characteristics
the carbon dioxide molecule is linear developed. Although the carbon oxygen connections are polar, their electrical dipole moments waive themselves by the molecule symmetry outward mutually, so that the molecule does not exhibit an electrical dipole moment. Nevertheless carbon dioxide is due to the internal dipole moments well in water soluble and absorbs some narrow parts of the electromagnetic spectrum within the range of the infrared radiation.
carbonic acid H
2 CO 3 forms chemical characteristics in water solved carbon dioxide, whereby however more than 99% of the carbon dioxide are only physically solved. Carbonic acid as such is appropriate forwards in an equilibrium with their dissociation products (species) for hydrogencarbonate (“Bicarbonat”, HCO 3 -) and carbonate (CO 3 2), those in one of the pH value dependent quantitative proportion to each other. If one intercepts the Oxonium - ions ( H +, actually H 3 O +) by addition of a caustic solution with hydroxyl ions ( OH -, formed with dissociation), then the quantitative proportion shifts to favour of carbonate.
use
carbon dioxide finds in the firm state of aggregation under the designation dry ice application in the technology. Dry ice melts not, but sublimated with −78 °C, however one can consolidate it below the critical temperature of 31 °C with pressure pressure to a colorless liquid. With the sublimation a white fog from that develops for cold CO 2 - air mixture and condensing air humidity, to which as effect in the stage technology employment finds.
Many beverages contain carbon dioxide, in order to obtain when drinking a better refreshment effect. With some beverages it develops by fermentation (beer, sparkling wine), with others it is artificially added (lemonade, soda water) or kohlendioxidhaltiges, natural mineral water is used. As food additive it carries the designation E 290. During the production carbon dioxide under high pressure is pumped to the beverage, whereby it reacts to approximately 0.2% with water to carbonic acid; the largest part is solved as gas in the water. With a decrease of pressure by opening the container it comes to a Nukleation, so that now the surplus loosened gas withdraws and ascends bläschenförmig. The bubbling of the gas and the säuerliche taste of carbonic acid on the tongue when drinking stimulate the taste sensory cells, which entails a refreshment effect.
Carbon dioxide is used also in fire extinguishers , since it oxygen of the fire source displaced (see also fire fighting, fire extinguishing agent).
Carbon dioxide is used as fertilizer in greenhouses. Reason is the CO 2 resulting from photo-synthetic consumption - lack with insufficient supply at fresh air, particularly in the winter when closed ventilation, because plants need CO 2 as basic substance. The carbon dioxide is brought in either directly as pure gas (relatively expensive) or as Verbrennungsprodukt from propane or natural gas (coupling of fertilization and heating). The possible yield increase depends on how strong the lack of CO is 2 and how strong the light offer for the plants is. Carbon dioxide is used also in the Aquaristik as fertilizer for aquatic plants (CO 2 - diffuser). Also by supply of organic substance that can be increased CO 2 - content in the water (respiration, but at expense of the oxygen content).
Supercritical carbon dioxide possesses a high solubility for nonpolar materials and can poisonous organic solvents replace. It is used as extracting agent, for example for the extraction of natural substances such as Koffein (production of koffeinfreiem coffee by Entkoffeinierung), and as solvent for cleaning and degreasing, for example of Wafern in the semiconductor industry and recently also of textiles (dry-cleaning). Up-to-date also intensively to it is researched to use supercritical carbon dioxide as reaction medium for the fine chemical production (e.g. .für the production of flavour materials) remain often active enzymes isolated there herein and remain no solvent arrears (contrary to organic solvents) in the products.
Carbon dioxide is used increasingly as natural refrigerant into air conditioning systems .
Carbon dioxide is used also as inert gas in the welding engineering - either in pure form or more frequently than additive to argon and/or helium. Since carbon dioxide is thermodynamically unstable at high temperatures, it does not become as inert gas, but when active gas marks.
CO 2 is used also in exhausting means (Zäpfchen). CO 2 is set free by a chemical reaction during the dissolution of the Zäpfchens and stretches the intestine, which releases again the chair reflex.
CO 2 in the atmosphere and greenhouse effect
estimation of the carbon dioxide emission in the European Union in the period of 1990 to 2020 (source: VGB registered association) |
Estimation of the world-wide carbon dioxide emission in the period 1990 to 2025 (source: VGB registered association) |
 Course that CO 2 - concentration in the atmosphere |
since beginning of the industrialization (approx. 1880) that rose CO 2 - portion in the atmosphere of approx. 280 ppm on 370 ppm (2005) [1] and rises z.Zt. further around on the average 1.5 ppm per year. This rise becomes essentially the CO caused by humans 2 - emissions of annually approx. 23 billion Tons (1990er years) attributed, from which about half remains in the atmosphere. Thus the highest concentration became for at least 420,000 years, probably even since 20 millions Years reaches (numbers from IPCC, S.38f; Conditions 2001).
However it lay in the carbon forwards approx. 300 millions Years probably at at least 1400 ppm. Earlier geological epochs can be compared however regarding the climatic effect with difficulty, since the oxygen portion had not stabilized yet ([2], [3] in [4]).
Carbon dioxide absorbs a part of the radiant heat (infrared radiation), during shorter-wave radiation, i.e. the largest part of the solar radiation, to happen can. This characteristic makes carbon dioxide a greenhouse gas in such a way specified. Together with water vapour it increases the middle temperature on the earth's surface of approx. -15°C on +15°C and is thus crucially jointly responsible for the life-friendly climate of the earth (natural greenhouse effect).
From many scientists the hypothesis will represent that one of humans leads caused increase that greenhouse gases in the atmosphere to the anthropogenen greenhouse effect so mentioned, which entails a climatic change (global heating up). The CO 2, which is set free by the burn of the fossil sources of energy oil, natural gas and coal , makes a substantial contribution in addition.
The contribution that CO 2 - release by humans to the greenhouse effect and/or. whether such is provable, and so that the negative consequences become, denied by climatic critics, which rejects therefore also climatic preventive measures as unnecessary.
Have the world-wide highest carbon dioxide output per inhabitant the USA, Canada, Finland, Tschechien and Belgium (conditions 2002), whereby in the future also the strongly growing industry of asiatic states will play a substantial role.
In principle exists over the necessity for the reduction of the CO 2 - output in the meantime large agreement. For this purpose some measures were already installed, which are not sufficiently regarded however of many as and also in their arrangement are partly violently disputed: internationally Kyoto minutes, however without participation of some important industrial nations like the USA, as well as on its basis the emission right trade in the European union. Also some methods of emission avoidance and/or. - connection such as CO 2 - attachment and afforestation are controversially discussed.
physiological effects and dangers
CO 2 - concentrations (volume %) in air and effects on humans:
- 0,05%: Natural concentration in air
- 0.15%: Hygenic interior air appoximate value for fresh air
- 0.3%: MIK - Worth, underneath its no health doubts during durable effect exist
- 0.5% (9 g/m ³): MAK - Limit value for daily exposition of 8 hours per day
- 1.5%: Increase of the breath time volume around more than 40%.
- 4%: Breathing air when breathing out
- 5%: Arise from headache, swindles and unconsciousness
- 8%: Unconsciousness, occurring death after 30 - 60 minutes
always again it comes to accidents with CO 2. In wine cellars, Futtersilos and liquid manure pits considerable quantities of CO 2 can form by Gärprozesse. During the fermentation of a litre Most (apple wine) develop for instance up to 50 litres fermenting gas. If not is provided for sufficient exhaust, dangerous concentrations form, due to the higher density of CO 2 compared with air particularly at ground level (“carbon dioxide lake”).
The direct side-effect on animal and humans can be based in individual cases on the displacement of the oxygen in air. The wide-spread opinion, CO 2 is actually innocuous and works only by displacing the vitally necessary oxygen, is however wrong. Therefore is not also the old “candle sample” goal-leading to recognizing dangerous oxygen scarceness. By the displacement of air (drop the O 2 - partial pressure to less than 130 mbar) by the heavier carbon dioxide it can come however additionally to the harmful effects of the CO 2 also to suffocating by oxygen deficiency.
In the blood solved CO 2 activated in more physiological (more naturally) and easily increased concentration the breath center of the brain, in clearly higher concentration leads it however to the reduction or even abolition of the reflektorischen incentive for breath (breath depression, respiratory arrest). These effects occur many more rapidly than an asphyxiation.
Starting from approximately 5 per cent of CO 2 in inhaled air headache and swindles arise, with higher concentrations accelerated heart impact (tachycardia), blood pressure rise, difficulty in breathing and unconsciousness (the CO in such a way specified 2 - Narkose). CO 2 - Concentrations of 8 per cent and more lead within 30 to 60 minutes to death.
Additionally carbon dioxide has an indirect effect on the oxygen household of the blood. Increases if carbon dioxide in air or in the Fischwasser is, then in the blood over the dissociation equilibrium of carbonic acid the pH value is decreased - the blood becomes “sour”. By this dropping the pH value hemoglobin is concerned. At lower pH value is reduced its O 2 - connection capacity. That is, with same O 2 - content of air can be bound and transported by hemoglobin less oxygen. This circumstances are described by the drilling effect and the Haldane effect. In the fabric, where the oxygen is to be delivered, the concentration of CO 2 is more highly (=niedriger pH value, smaller O 2 - connection capacity) and relieved thereby the O 2 - delivery. In the lung conditions turned around and favour so a “loading” of hemoglobin with oxygen.
This indirect effect over the pH value of the blood is to be differentiated from the stronger Giftigkeit carbon monoxide. Carbon monoxide masks as a complexing agent reversibly the iron core hemoglobin and prevents thereby the connection of oxygen in the red blood corpuscles. This is another (more effective) molecular mechanism than with the carbon dioxide.
Whole families of a fermenting gas poisoning fall again and again to the victim, because several persons inhale with the rescue of a family member carbon dioxide and become unconscious. The Ersthelfer goes with a rescue attempt only in danger - nobody can carry an unconscious one from a cellar with stopped breath. To be set off instead a ventilation (if available) is to be switched on and an emergency call.
The rescue of a had an accident one from CO 2 - is possible for suspicious situations (wine cellar etc.) only for professional task forces (fire-brigade) with heavy respiratory protection.
In rare cases it comes also to natural catastrophes with carbon dioxide; the most well-known itself 1986 at the Nyos lake in Cameroon, occurred.
see also
- air
- Pasteur effect
- CO2-Partialdruck see partial pressure
- emission right trade
- CO2-Sequestrierung
- CO2-Neutralität
- Boudouard equilibrium
to literature
- Eike Roth: Global environmental problems - causes and solutions. Friedmann, Munich 2004. (Greenhouse effect, including its causing and discussion of the anthropogenen influence.) ISBN 3-933431-31-X
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