What is carbon dioxide and how was it discovered?
Joseph Black, a Scottish chemist and physician, first identified carbon dioxide in the 1750s. At room temperatures (20-25 oC), carbon dioxide is an odourless, colourless gas, which is faintly acidic and non-flammable.
Carbon dioxide is a molecule with the molecular formula CO2. The linear molecule consists of a carbon atom that is doubly bonded to two oxygen atoms, O=C=O.
Although carbon dioxide mainly consists in the gaseous form, it also has a solid and a liquid form. It can only be solid when temperatures are below -78 oC. Liquid carbon dioxide mainly exists when carbon dioxide is dissolved in water. Carbon dioxide is only water-soluble, when pressure is maintained. After pressure drops it will try to escape to air, leaving a mass of air-bubbles in the water.
Where on earth do we find carbon dioxide?
Carbon dioxide can be found mainly in air, but also in water as a part of the carbon cycle. We can show you how the carbon cycle works, by means of an explanation and a schematic representation.
Applications of carbon dioxide by humans
Humans use carbon dioxide in many different ways. The most familiar example is its use in soft drinks and beer, to make them fizzy. Carbon dioxide released by baking powder or yeast makes cake batter rise.
Some fire extinguishers use carbon dioxide because it is denser than air. Carbon dioxide can blanket a fire, because of its heaviness. It prevents oxygen from getting to the fire and as a result, the burning material is deprived of the oxygen it needs to continue burning.
Carbon dioxide is also used in a technology called supercritical fluid extraction that is used to decaffeinate coffee. The solid form of carbon dioxide, commonly known as Dry Ice, is used in theatres to create stage fogs and make things like "magic potions" bubble. Carbon Dioxide starts to get highlight in the modern Health science as well by its remarkable effect on the Human Body.
The part carbon dioxide plays in environmental processes
Carbon dioxide is one of the most abundant gasses in the atmosphere. Carbon dioxide plays an important part in vital plant and animal process, such as photosynthesis and respiration. These processes will be briefly explained here.
Green plants convert carbon dioxide and water into food compounds, such as glucose, and oxygen. This process is called photosynthesis.
The reaction of photosynthesis is as follows: 6 CO2 + 6 H2O --> C6H12O6 + 6 O2
Plants and animals, in turn, convert the food compounds by combining it with oxygen to release energy for growth and other life activities. This is the respiration process, the reverse of photosynthesis.
The respiration reaction is as follows: C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O
Photosynthesis and respiration play an important role in the carbon cycle and are at equilibrium with one another.
Photosynthesis dominates during the warmer part of the year and respiration dominates during the colder part of the year. However, both processes occur the entire year. Overall, then, carbon dioxide in the atmosphere decreases during the growing season and increases during the rest of the year.
Because the seasons in the northern and southern hemispheres are opposite, carbon dioxide in the atmosphere is increasing in the north while decreasing in the south, and vice versa. The cycle is more clearly present in the northern hemisphere; because it has relatively more land mass and terrestrial vegetation. Oceans dominate the southern hemisphere.
Properties of carbon dioxide
There are several physical and chemical properties, which belong to carbon dioxide. Here we will sum them up in a table.
| Properties | Value |
| Molecular weight | 44.01 |
| Specific gravity | 1.53 at 21 oC |
| Critical density | 468 kg/m3 |
| Concentration in air | 370,3 * 107 ppm |
| Stability | High |
| Liquid | Pressure < 415.8 kPa |
| Solid | Temperature < -78 oC |
| Henry constant for solubility | 298.15 mol/kg * bar |
| Water solubility | 0.9 vol/vol at 20 oC |