Carbon dioxide

Chemical and physical properties

Carbon dioxide is a colorless gas which, when inhaled at high concentrations (a dangerous activity due to the associated asphyxiation risk), produces a sour taste in the mouth and stinging sensation in the nose and throat. These effects result from the gas dissolving in the mucous membranes and saliva, forming a weak solution of carbonic acid.

Related Topics:
Color - Asphyxiation - Mucous membranes - Carbonic acid

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Its density at 25 °C is 1.98 kg m−3, about 1.5 times that of air. The carbon dioxide molecule (O=C=O) contains two double bonds and has a linear shape. It has no electrical dipole. As it is fully oxidized, it is not very reactive and in particular not flammable.

Related Topics:
Air - Double bonds - Dipole - Flammable

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At temperatures below −78 °C, carbon dioxide condenses into a white solid called dry ice. Liquid carbon dioxide forms only at pressures above 5.1 atm; at atmospheric pressure, it passes directly between the gaseous and solid phases in a process called sublimation.

Related Topics:
Dry ice - Atm - Sublimation

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Water will absorb its own volume of carbon dioxide, and more than this under pressure. About 1% of the dissolved carbon dioxide turns into carbonic acid. The carbonic acid in turn dissociates partly to form bicarbonate and carbonate ions.

Related Topics:
Water - Volume - Carbonic acid - Bicarbonate - Carbonate - Ion

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Test For This Gas

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When a lighted splint is inserted into a test tube containing this gas, it is immediately extinguished, as carbon dioxide does not support combustion. (Certain fire extinguishers contain carbon dioxide to extinguish the flame). To further confirm that the gas is carbon dioxide, the gas may be bubbled into calcium hydroxide solution. The calcium hydroxide turns milky due to the formation of calcium carbonate.

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