Iodine may be prepared by displacement from its compounds with chlorine. Treating an iodide with manganese dioxide and sulfuric acid sublimes the iodine. Iodine is important in medical treatment; tincture of iodine and iodoform are widely used. Iodine is employed in the preparation of certain drugs and in the manufacture of some dyes.
Silver iodide, a yellow salt, is used in photography; it is water insoluble and turns black when exposed to light. Starch turns deep blue almost black in the presence of a small amount of iodine; this reaction serves as a test for either starch or iodine.
Iodine in small amounts is essential to human nutrition; in the thyroid gland it becomes a part of the iodine-containing hormones. Goiter, a swelling of the thyroid, is often a symptom of inadequate iodine in the diet.
Iodine has only one stable isotope, iodine—; it is the only isotope of iodine occurring in nature, although 24 iodine isotopes are known.
Iodine— is a radioactive isotope with a half-life of 8 days. In this activity, students see colours change in a solution, and learn how chemistry can explain this magical result.
This trick works because iodine is brown when dissolved in water and purple when dissolved in oil. When you shake the fluids, the iodine leaves the water and dissolves in the oil, and returns to its purple colour! The reason the iodine molecules leave water to dissolve in oil is due to how polarity affects solubility. Water is polar; it has an uneven distribution of electrons. Oil is non-polar; electrons in molecules of this substance are distributed evenly.
Iodine is also a non-polar molecule therefore it is more soluble in oil; "like dissolves like". Explain the importance of observation when doing science. What colour changes did you notice?
What part of the mixture is causing the colour change? This misconception arises because the small amount of vapor produced has such a deep colour that the liquid appears not to form. In fact, if iodine crystals are heated carefully to just above their melting point of Iodine was discovered by Bernard Courtois in He was born to a manufacturer of saltpeter a vital part of gunpowder. At the time of the Napoleonic Wars , France was at war and saltpeter was in great demand.
Saltpeter produced from French niter beds required sodium carbonate, which could be isolated from seaweed washed up on the coasts of Normandy and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash then washed with water. The remaining waste was destroyed by adding sulfuric acid.
One day Courtois added too much sulfuric acid and a cloud of purple vapor rose. Courtois noted that the vapor crystallized on cold surfaces making dark crystals.
Courtois suspected that this was a new element but lacked the money to pursue his observations. They described the substance to a meeting of the Imperial Institute of France. On December 6, Gay-Lussac announced that the new substance was either an element or a compound of oxygen. Davy did some experiments on the substance and noted its similarity to chlorine.
Davy sent a letter dated December 10 to the Royal Society of London stating that he had identified a new element. A large argument erupted between Davy and Gay-Lussac over who identified iodine first but both scientists acknowledged Courtois as the first to isolate the chemical element. Iodine is used in pharmaceuticals, antiseptics, medicine, food supplements, dyes, catalysts, halogen lights, photography, water purifying, and starch detection.
Iodine naturally occurs in the environment chiefly as dissolved iodide in seawater , although it is also found in some minerals and soils. The element may be prepared in an ultrapure form through the reaction of potassium iodide with copper II sulfate. There are also a few other methods of isolating this element in the laboratory-- for example the method used to isolate other halogens: oxidation of the iodide in hydroiodic acid often made in situ with an iodide and sulfuric acid by manganese dioxide see below in Descriptive chemistry.
Although the element is actually quite rare, kelp and certain plants and algae have some ability to concentrate iodine, which helps introduce the element into the food chain. Iodine is found in the mineral caliche , found in Chile , between the Andes and the sea.
It can also be found in some seaweeds as well as extracted from seawater. Extraction from seawater involves electrolysis. The brine is first purified and acidified using sulphuric acid and is then reacted with chlorine. An iodine solution is produced but it is yet too dilute and has to be concentrated. To do this air is blown into the solution which causes the iodine to evaporate, then it is passed into an absorbing tower containing acid where sulfur dioxide is added to reduce the iodine.
Another source is from kelp. This source was used in the 18th and 19th centuries but is no longer economically viable. By contrast with chlorine , the formation of the hypohalite ion IO — in neutral aqueous solutions of iodine is negligible.
Solubility in water is greatly improved if the solution contains dissolved iodides such as hydroiodic acid , potassium iodide , or sodium iodide ; this extra solubility results from the high solubility of the I 3 - ion.
Dissolved bromides also improve water solubility of iodine. Iodine is soluble in a number of organic solvents, including ethanol Solutions in chloroform, carbon tetrachloride, and carbon disulfide are violet.
Elemental iodine can be prepared by oxidizing iodides with chlorine:. Iodine is reduced to hydroiodic acid by hydrogen sulfide : [3]. Iodine is oxidized to iodate by nitric acid : [4]. Iodine is converted in a two stage reaction to iodide and iodate in solutions of alkali hydroxides such as sodium hydroxide : [1].
See also iodine compounds.
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