Chlorine has a characteristic penetrating and irritating odor. The gas is greenish yellow in color and the liquid is clear amber. The data on physical properties of chlorine as determined by different investigators show some variations.
Atomic and Molecular Properties
- Atomic Symbol - Cl
- Atomic Weight - 35.453
- Atomic Number - 17
- Molecular Weight of Cl2 - 70.906
Chlorine is neither explosive nor flammable. Chlorine will support combustion under certain conditions. Many materials that burn in oxygen (air) atmospheres will also burn in chlorine atmospheres. Many organic chemicals react readily with chlorine, sometimes violently. An important specific compound of concern is hydrogen. Chlorine reacts explosively with hydrogen in a range of 4% to 93% hydrogen. The reaction is initiated very easily much the same way as hydrogen and oxygen. See Pamphlet 121 for more information.
Chlorine usually forms compounds with a valence of -1 but it can combine with a valence of +1, +2, +3, +4, +5, or +7.
Reactions with Water
Chlorine is only slightly soluble in water (0.3% to 0.7%) depending on the water temperature. However the resulting water phase is extremely corrosive, see Reactions with Metals below.
Reactions with Metals
The reaction rate of dry chlorine with most metals increases rapidly above a temperature which is characteristic for the metal. Two of the more common metals are titanium and steel. In the presence of dry chlorine, titanium is flammable. Care should be taken to make sure titanium materials are not used in dry chlorine service. Steel is the most common material used in dry chlorine service. At temperatures above 300°F (149°C) a chlorine/steel fire can result. It is important to make sure steel in chlorine service does not go above this temperature either through internal/external heating or mechanical abrasion. Moist chlorine, primarily because of the hydrochloric and hypochlorous acids formed through hydrolysis, is very corrosive to most common metals. Platinum, silver, tantalum and titanium are resistant. Consult CI Pamphlet 6 (11.1) for detailed information on reactivity with metals.
Reactions with Organic Compounds
Chlorine reacts with many organic compounds to form chlorinated derivatives. Some reactions can be extremely violent, especially those with hydrocarbons, alcohols and ethers. Proper methods must be followed, whether in laboratory or plant, when organic materials are reacted with chlorine.
See CI Pamphlet 1.