Iodine solubility

Ramette, R.W. and Sandford, R.W., Jr. Thermodynamics of iodine solubility and triiodide ion formation in water and deuterium... 

It is not clear, however, in which chemical state the particulate iodine is present. Some studies reported it to be 103 but in others no 103 was found (see references and discussion in McFiggans et al. (2000)). Based on measurements of aerosol composition. Baker et al. (2000) state that iodine is present in aerosol in varying proportions as soluble inorganic iodine, soluble organic iodine and insoluble, or unextractable, iodine. Baker et al. (2001) measured the deposition of iodine in rainwater and in aerosol at Weyboume, North coast of Norfolk, UK. They found that iodide (I ) constituted 5-100% of total iodine deposition in both rain and aerosol. The rest was found to be iodate (10j") with a very small contribution from CH3I (<3% of the total iodine deposition). 

Properties White crystals unpleasant odor. Mp 78.5C (decomposes). Light acts upon it, causing a gradual change in color to red and a separation of iodine. Soluble in alcohol, ether, benzene insoluble in water. 

More metallic than iodine. Soluble in organic solvents. Due to short half-life of isotopes, only a few physical properties can be measured. Chemical studies are carried out on trace amounts (< ]0-6M solos). HAt, CHjAt. AtCl, AtBr, Atl have been identified by time-of-flight mass spectrometry Appleman et al. Inorg. Chem. 5, 766 (1966). Oxidation states —l, O, +5 existence of +1, +3, +7 oxidation... 

Dark.brown powder evolves oxygen when heated, first forming Pb,0., at high temp PbO. d 9.38. in sol in water sol in HC1 with evolution of Cl in dil HNO in presence of HjOlP oxalic acid, or other reducers sol in alkali iodide solns with libaration of iodine soluble in hot caustic alkali solns. LDm i.p. in guinea pigs 200 mg/kg, Handbook of Toxicology vol, 1, W. S. Spector, Ed. (Saunders, Philadelphia, 1956) pp 176-177. 

Unlim. A soup coiitaining iodine is sometimes used in scrofulous skin diseases. It should contain some 3 per cent, iodine, while potassium iodides should also added to render the iodine soluble. 

When sulphur is melted viscosity changes occur as the temperature is raised. These changes are due to the formation of long-chain polymers (in very pure sulphur, chains containing about 100 (X)0 atoms may be formed). The polymeric nature of molten sulphur can be recognised if molten sulphur is poured in a thin stream into cold water, when a plastic rubbery mass known as plastic sulphur is obtained. This is only slightly soluble in carbon disulphide, but on standing it loses its plasticity and reverts to the soluble rhombic form. If certain substances, for example iodine or oxides of arsenic, are incorporated into the plastic sulphur, the rubbery character can be preserved. 

This reaction is also used on a large scale, to obtain iodine from seaweed. The ash from burnt seaweed ( kelp ) is extracted with water, concentrated, and the salts other than iodides (sulphates and chlorides) crystallise out. The more soluble iodides remain and the liquor is mixed with sulphuric acid and manganese dioxide added the evolved iodine distils off and is condensed. 

Like bromine, iodine is soluble in organic solvents, for example chloroform, which can be used to extract it from an aqueous solution. The iodine imparts a characteristic purple colour to the organic layer this is used as a test for iodine (p. 349). NB Brown solutions are formed when iodine dissolves in ether, alcohol, and acetone. In chloroform and benzene a purple solution is formed, whilst a violet solution is produced in carbon disulphide and some hydrocarbons. These colours arise due to charge transfer (p. 60) to and from the iodine and the solvent organic molecules. 

To determine which halogen is present, take 1-2 ml. of the filtrate from the sodium fusion, and add dilute sulphuric acid until just acid to litmus. Add about 1 ml. of benzene and then about 1 ml. of chlorine water and shake. A yellowish-brown colour in the benzene indicates bromine, and a violet colour iodine. If neither colour appears, the halogen is chlorine. The result may be confirmed by testing the solubility of the silver halide (free from cyanide) in dilute ammonia solution silver chloride is readily soluble, whereas the bromide dissolves with difficulty, and the iodide not at all. 

When polymers or other water-soluble substances are present in the sample, it is advantageous to add a small amount of chloroform to the initial reaction mixture after the subsequent addition of water, a two-phase system results which may be titrated in the usual way to a starch end point or by observing the disappearance of the iodine colour in the chloroform layer. 

Nitrogen and sulphur absent, (i) If only one halogen is present, acidify with dilute nitric acid and add excess of silver nitrate solution. A precipitate indicates the presence of a halogen. Decant the mother liquor and treat the precipitate with dilute aqueous ammonia solution If the precipitate is white and readily soluble in the ammonia solution, chlorine is present if it is pale yellow and difficultly soluble, bromine is present if it is yellow and insoluble, then iodine is indicated. Iodine and bromine should be confirmed by the tests given below. 

Iodine is a bluish-black, lustrous solid, volatizing at ordinary temperatures into a blue-violet gas with an irritating odor it forms compounds with many elements, but is less active than the other halogens, which displace it from iodides. Iodine exhibits some metallic-like properties. It dissolves readily in chloroform, carbon tetrachloride, or carbon disulfide to form beautiful purple solutions. It is only slightly soluble in water. 

Suspend 5 g of soluble starch in 50 mL of saturated NaCl solution, and stir slowly into 500 mL of boiling saturated NaCl solution. Cool and bottle. Free iodine produces a blue-black color. 

Starch solution (iodine indicator) dissolve 5 g of soluble starch in cold water, pour the solution into 2 liters of water and boil for a few minutes. Keep in a glass-stoppered bottle. 

Because of iodine s poor solubility, solutions are prepared by adding an excess of I-. The complexation reaction... 

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