Iodine is a gray-violet[2] solid. It is also anonmetal and ahalogen. It sublimes when heated to make a bright purple vapor. This vapor is very irritating, although colorful. Iodine does not dissolve in water, but it does dissolve in asolution of aniodide in water. It dissolves easily inorganicsolvents.
Potassium iodide is one of the most common iodides. Iodides are normally colorless but turn yellow after being in air because the iodide isoxidized to iodine. Iodides react withacidifiedmanganese dioxide orchlorine to make iodine. Iodine monochloride is a red or brown liquid. Iodine trichloride, as well asiodine trifluoride, are yellow solids.Iodates likepotassium iodate are colorless solids similar tochlorates. Iodic acid is the only stable oxidizing halogen acid.Chloric acid, by comparison, is very unstable and dangerous. Iodine pentoxide is a white solid, and iodine pentafluoride is a yellowish liquid. Periodates, likesodium periodate, are colorless solids similar toperchlorates, although weaker oxidizing agents. They decompose to iodates when they are heated. Periodic acid is not as stable as iodic acid. Iodine heptafluoride is the only iodine(VII) compound.
It was discovered byBarnard Courtois in1811. He burnedseaweed to getsodium carbonate and reacted the residue withsulfuric acid. One time, he poured too much sulfuric acid on the seaweed and purple vapor came out which made dark blue-black crystals on a cold surface. He did not have enough money to see whether it was a new element or not. He gave samples to several chemists, who identified it as an element in1813.
Iodine is too reactive to be in nature as an element. Iodine compounds are not common in the ground. There is a mineral calledcaliche that is found in dry deserts. It has iodate in it. Iodide is found in seawater.Kelp has quite large amounts of iodine in it. Iodine is one of the heaviest elements needed by living things. If people do not get enough of it, they get a disease known asgoitre. Mostsalt has iodinein it, in the form of iodide or iodate. People can also take iodine pills to make sure they get enough.
Kelp was burned and the iodine extracted from the ashes in the 18th and 19th century, but now it is not good enough for common use. Most iodine now is extracted from seawater. Chlorine is reacted with seawater to change the iodide to iodine. Air is blown over the water to evaporate the iodine. Then the iodine is reduced withsulfur dioxide to hydriodic acid. Then the hydriodic acid is oxidized with chlorine again to make iodine. This process is repeated until the iodine is pure.
A very pure form of iodine is made by reactingcopper sulfate and potassium iodide. This makes copper(II) iodide which is not stable. It breaks down intocopper(I) iodide and iodine, which is pure.
Iodine is used as acatalyst for makingacetic acid.Animal feed also has iodine in it fornutrition. Iodine is used for adisinfectant.Tincture of iodine is a common iodine disinfectant. Iodine can be used to preventthyroid cancer after a nuclear explosion. After a nuclear explosion, radioactive iodine fills the air. The radioactive iodine easily goes into the thyroid and causes cancer. When people take iodine tablets, it fills up the thyroid with non-radioactive iodine which prevents any radioactive iodine from coming in.
Iodine compounds can be used inX-rays because X-rays cannot go through them easily. Some metals are purified using their iodides. Silver iodide is used inphotographic film andcloud seeding. Erythrosine is a food coloring that has iodine in it. Iodine can be used to make illegal drugs so it is restricted in some areas. Iodine can be used as a test for reducing agents. Iodine turns colorless when mixed with a reducing agent. Iodine also turns black when mixed with starch. Iodides become colored when mixed with oxidizing agents.
Iodine can irritate skin. Its vapors are irritating to the lungs. It is less toxic than the other halogens, though. 2-3 grams of iodine can kill. Iodides are only toxic in large amounts.
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