industrially important H 2 and caustic soda (NaOH) are also produced (Section 21-4).
More than 26 billion pounds of chlorine was produced in the United States in 1997.
Chlorine is used to produce many commercially important products. Tremendous
amounts of it are used in extractive metallurgy and in chlorinating hydrocarbons to produce
a variety of compounds (such as polyvinyl chloride, a plastic). Chlorine is present as Cl 2 ,
NaClO, Ca(ClO) 2 , or Ca(ClO)Cl in household bleaches as well as in bleaches for wood
pulp and textiles. Under carefully controlled conditions, Cl 2 is used to kill bacteria in
public water supplies.
Bromine
Bromine (Greek bromos,“stench”) is less abundant than fluorine and chlorine. In the
elemental form it is a dense, freely flowing, corrosive, dark-red liquid with a brownish red
vapor at 25°C. It occurs mainly in NaBr, KBr, MgBr 2 , and CaBr 2 in salt water, under-
ground salt brines, and salt beds. The major commercial source for bromine is deep brine
wells in Arkansas that contain up to 5000 parts per million (0.5%) of bromide.
Bromine is used in the production of silver bromide for light-sensitive eyeglasses and
photographic film; in the production of sodium bromide, a mild sedative; and in methyl
bromide, CH 3 Br, a soil fumigant that contributes to the destruction of the ozone layer.
Iodine
Iodine (Greek iodos,“purple”) is a violet-black crystalline solid with a metallic luster. It
exists in equilibrium with a violet vapor at 25°C. The element can be obtained from dried
seaweed or shellfish or from NaIO 3 impurities in Chilean nitrate (NaNO 3 ) deposits. It is
contained in the growth-regulating hormone thyroxine, produced by the thyroid gland.
“Iodized” table salt is about 0.02% KI, which helps prevent goiter, a condition in which
the thyroid enlarges. Iodine has been used as an antiseptic and germicide in the form of
tincture of iodine, a solution in alcohol.
The preparation of iodine involves reduction of iodate ion from NaIO 3 with sodium
hydrogen sulfite, NaHSO 3.
2IO 3 (aq)5HSO 3 (aq)88n3HSO 4 (aq)2SO 42 (aq)H 2 O()I 2 (s)Iodine is then purified by sublimation (Figure 13-16).
24-4 Occurrence, Production, and Uses 947Chlorides occur in salt beds.
Bromine is a dark red, volatile liquid.Iodine reacts with starch (as in this
potato) to form a deep-blue complex
substance.More recently available is an aqueous
solution of an iodine complex of
polyvinylpyrrolidone, or “povidone.” It
does not sting when applied to open
wounds.