Products
Carbon dioxide is commercially available in compressed gas cylinders liquefied and as dry ice, among other products. The various products differ in purity. Carbon dioxide is also monographed in the pharmacopoeia. It is available, for example, in grocery stores for making your own sparkling water.
Structure
Carbon dioxide (CO
2
, O=C=O, M
r
= 44.01 g/mol) exists as a colorless, nonflammable, and at low concentrations odorless gas that is somewhat soluble in water. It is a linear molecule consisting of one carbon atom covalently bonded to two oxygen atoms. Under pressure, the gas liquefies. Solid carbon dioxide is called dry ice. It sublimates at -78.5°C, i.e. it passes directly from the solid to the gaseous state. Carbon dioxide is a natural gas that belongs to the carbon cycle. Since the beginning of the industrial revolution, CO
2
–concentration in the atmosphere has risen sharply, by more than a third, to over 412 ppm today (source: NASA).
Properties and reactions
Carbon dioxide is formed when acids react with carbonates such as calcium carbonate:
- 2 HCl (hydrochloric acid) + CaCO
3
(calcium carbonate, lime) CO
2
(carbon dioxide) + CaCl
2
(calcium chloride) + H
2
O (water)
Carbonic acid is required by plants in photosynthesis for the synthesis of carbohydrates as a substrate:
- 6 CO
2
(carbon dioxide) + 6 H
2
O (water) C
6
H
12
O
6
(glucose) + O
2
(oxygen)
Conversely, humans consume the oxygen released in the process to produce energy from carbohydrates:
- C
6
H
12
O
6
(glucose) + 6 O
2
(oxygen) 6 CO
2
(carbon dioxide) + 6 H
2
O (water)
Carbon dioxide is released when organic compounds are burned and heat and energy are obtained (e.g. wood, coal, gas, kerosene, gasoline, diesel, oil). Using methane as an example:
- CH
4
(methane) + 2 O
2
(oxygen) CO
2
(carbon dioxide) + 2 H
2
O (water)
During alcoholic fermentation (fermentation) is formed by yeast fungi ethanol and carbon dioxide. This plays an important role, for example, in the production of beer or the rising of breads. Organic material is broken down by fungi and is available again for the carbon cycle:
- C
6
H
12
O
6
(glucose) 2 CO
2
(carbon dioxide) + 2 C
2
H
6
O (ethanol)
Carbon dioxide can be released from carbonates and hydrogen carbonates during heating:
- CaCO
3
(calcium carbonate) CaO (calcium oxide) + CO
2
(carbon dioxide)
Carbonic acid is formed when carbon dioxide (CO
2
) is dissolved in water. The following equilibrium is formed:
- CO
2
(carbon dioxide) + H
2
O (water) ⇌ H
2
CO
3
(carbonic acid)
The reaction leads to a slight acidification of water due to deprotonation:
- H
2
CO
3
(carbonic acid) ⇌ HCO
3
–
(hydrogen carbonate) + H
+
⇌ CO
3
2-
(carbonate) + H
+
Calcium hydroxide can be used to bind carbon dioxide:
- Ca(OH)
2
(calcium hydroxide) + CO
2
(carbon dioxide) CaCO
3
(calcium carbonate) + H
2
O (water)
Fields of application (selection)
- Medical in combination with oxygen to stimulate breathing after respiratory arrest (eg, carbogen).
- As a laxative in the form of suppositories (eg, lecicarbon, formation from sodium hydrogen carbonate).
- Carbon dioxide is released from various antacids.
- In the dissolution of effervescent tablets and effervescent powders.
- Operating principle of baking soda.
- For chemical syntheses, as solvents and extraction agents.
- For the production of sparkling water, as an acidity regulator, as a propellant gas, inert gas and coolant in food technology.
- Carbonates and hydrogen carbonates play an important role in pharmacy as active ingredients and especially as excipients (eg calcium carbonate, sodium carbonate, potassium carbonate and sodium hydrogen carbonate.
Adverse effects
High concentrations of carbon dioxide cause asphyxiation in humans because oxygen is displaced. Contact with the liquefied gas causes frostbite. Pressurized containers can explode if heated. Carbon dioxide is the most important greenhouse gas. Global warming is a result of the uncontrolled release of the gas into the atmosphere. The main causes are the burning of fossil fuels, industrial processes, and global deforestation and forest clearance. Unchecked global warming is expected to cause dramatic changes on Earth in the future. The excessively produced carbon dioxide also dissolves in the water of the oceans, leading to acidification due to the formation of carbonic acid and its dissociation, threatening marine life.
