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Extraction of Halogens: Iodine and Chlorine.

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Introduction

Extraction of Halogens: Iodine and Chlorine A method of extracting chlorine is via the membrane cell. This process is described below: On one side circulating brine is in contact with a titanium anode and chloride ions are discharged producing chlorine gas: 2Na+ (aq) + 2Cl-(aq) 2Na+ (aq) + Cl2 (g) + 2e- A steel cathode supplies electrons to the water to liberate hydrogen gas and hydroxide ions: 2Na+ (aq) + 2H2O (l) + 2e- 2Na+ (aq) + H2 (g) + 2OH-(aq) Any chemical reaction which involves oxidation and reduction is described as a redox reaction. This therefore causes the above reactions to also be described at redox reactions as reduction and oxidation are taking place. [3] In the process of extraction of halogens it is necessary to keep apart the products formed at both the cathode and anode in order to prevent them reacting. A mercury cathode cell can be used to achieve this, as the products are produced in different containers. Electrolysis takes place in the first container; this contains anodes coated with a metal oxide; Chlorine ions are discharged here. ...read more.

Middle

This method of burning kelp lasted until 1930. Extraction of iodine from brine and nitrate ores has become the two major sources of the element most recently. Both of these extractions occur due to redox reactions and can be shown by the following reactions: Step One. Brine is reacted with chlorine: 2I- (aq) + Cl2 (g) I2 (aq) + 2Cl- (aq) Step Two. Sulphur dioxide is added to reduce vaporised iodine: SO2 (g) + I2 (aq) + H2O (l) 2H+ (aq) + 2I- (aq) + H2SO4 (aq) Step one is now repeated to form a higher concentration of iodine than its solubility, so that iodine crystals separate and can be recovered by filtration. From Nitrate ores, iodine is formed from iodate (V) ions IO3- (Sodium iodate (V)). During this method, sodium nitrate ore is leached with water which results in the sodium nitrate to crystallise when cooling. After these crystals are separated, a spray of this solution I passed into sulphur dioxide with reduces the iodate (V) ions. IO3- (aq) ...read more.

Conclusion

This therefore would cause the iodine to be contaminated and extremely dilute. * In connection with the nitrate ore, if electrodes were used to extract iodine, nitrate would also be formed alone with iodine. It is evident from the following diagram that as nitrate is a negatively charged ion it would also be discharged at the anode. This therefore results in the present methods of extracting iodine to be used as it allows a high concentration of uncontaminated iodine to be formed. Each of the processes used for both halogens are extremely efficient. Membrane cell used for nitrate ore Substance Annual mass used in the world Percentage Applications Chlorine 39 million tonnes 27% 17% 16% 13% 6% 21% chloroenthane, chloromethanes, solvents (e.g. CHCl=CCl2), inorganixs (e.g. HCl,NaClO), propene oxide, miscellaneous compounds (e.g. water purification, insecticides). Iodine [1] 13 000 tonnes 25% 15% 15% 15% 10% 20% pharmaceutical products, used as catalysts, an ingredient of printing inks and dyes, animal feedstuffs, photographic chemicals, miscellaneous compounds. Hydrogen 36 million tonnes 53% 20% 7% 20% ammonia, oil refinery processes, methanol, other processes. Sodium hydroxide 41 million tonne 30% 16% 5% 5% 5% 5% 34% manufacture of chemicals (e.g. ...read more.

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