Iodine exists in nature as soluble in water. It is rare in nature. Except for the high content of iodine in sea water, kelp, fish, shellfish and other animals and plants (50-60 micrograms per liter of sea water), the content in most soil, rock and water is very low.
Iodine is scarce in nature and ranks 47th in the earth's crust. Except for the high content in seawater (50-60 micrograms per liter of seawater), the content in most soil, rock and water is very low.
The source of iodine in nature is mainly in the form of sodium iodate NaIO3 in Chile's saltpeter ore. The content of iodine in seawater is very small, but some organisms in the sea (such as algae, kelp, etc.) have the ability to selectively absorb and enrich iodine, which is an important source of iodine.
Role and use of iodine:
Iodine is extremely important for the life of animals and plants. The iodide and iodate in seawater enter the metabolism of most marine organisms. In advanced mammals, iodine is concentrated in the thyroid in the form of iodized amino acids, and iodine deficiency will cause goiter. About 2/3 of iodine and compounds are used to prepare preservatives, disinfectants and drugs, such as iodine tincture and iodoform CHI3. The intake of sodium iodate as a food additive to supplement iodine is insufficient. Radioisotope iodine-131 is used in radiotherapy and radiotracer technology. Iodine can also be used to make dyes and photographic films.
Iodine and its related compounds are mainly used in medicine, photography and dyes. It can also be used as a tracer for systematic monitoring, such as for geothermal system monitoring. Silver iodide (AgI) can be used not only as a photosensitive agent for photographic film, but also as a crystal seed for cloud formation during artificial rainfall. The alcohol solution of I2 and KI, namely iodine liquor, is a commonly used disinfectant; Iodoform (CHI3) is used as a preservative.
Calibrate sodium thiosulfate standard solution. Determine the iodine value of oil. Color reaction of magnesium and acetate. Manufacture iodane and iodide, etc. Colorimetric determination of starch. Non-protein nitrogen and amylase in serum were measured. Preparation of solid violet and toluidine blue iodine solution, catalyst and disinfectant.
Iodine-containing preparations such as iodine tincture, compound iodine solution, iodine throat tablets, iodine glycerin and so on are widely used in medical treatment, and iodine tincture is a common disinfectant in the family.
On November 18, 2021, an engineering study published by the British journal Nature pointed out that the use of iodine in electric propulsion systems instead of xenon, which is more expensive and difficult to store, could improve the performance of spacecraft. The iodine-powered spacecraft completed the in-orbit test for the first time, accelerating the acceptance of alternative propellants in the aerospace industry.
Physiological function of iodine:
Iodine is closely related to human health. Adults contain 20-50mg of iodine, which is essential for maintaining normal thyroid function. When the body lacks iodine, it will suffer from goiter. Therefore, iodide can prevent and treat goiter. Eating more iodine-rich foods such as kelp and fish is also very effective in preventing and treating goiter. Iodine radioisotope I can be used for early diagnosis and treatment of thyroid tumors.
Iodine is one of the essential trace elements of the human body, known as "intelligence element". The total amount of iodine in healthy adults is about 30 mg (20~50 mg), of which 70%~80% is in the thyroid gland.
Chemical properties of iodine:
The chemical property of iodine is not as active as that of the same group elements F2, Cl2 and Br2, but it can also show various oxidation states from - 1 to+7 in chemical reactions. Its chemical properties can be summarized as follows.
The reason why iodine can be dissolved in iodide is that I2 and iodine ions form wrong ions. In this equilibrium, there is always iodine in the solution, so many potassium iodide solutions have the same properties as iodine solutions. Iodine molecule will form blue-black complex with starch, but iodine ion I⁻ will not.
Reaction of iodine with metal:
Generally, metals that can react with chlorine (except noble metals) can also react with iodine, but their reactivity is not as active as chlorine. For example, iodine can react directly with active metals at room temperature, and the reaction with other metals can only take place at a higher temperature. I2 + 2Na→ 2NaI.
Reaction of iodine with nonmetals:
Generally, nonmetals that can react with chlorine can also react with iodine. Because the oxidation ability of iodine is weak and the reaction activity is less than that of chlorine, the reaction can only take place at a higher temperature. For example, it interacts with phosphorus and only generates phosphorus triiodide: 3I2+2P → 2PI3.
Reaction of iodine with water:
(1) Reaction type of halogen and water: self oxidation and reduction reaction will occur in water.
(2) Reaction of iodine with water: the solubility of iodine in water is the smallest, only slightly soluble in water, and the solubility is 0.029g/100g water. I2 and water can not undergo the oxidation-reduction reaction like F2 and water. Iodine will precipitate when oxygen is introduced into the hydrogen iodide solution:
4HI + O2 → 2I2 + 2H2O
Under alkaline conditions, I2 can undergo its own redox reaction to generate iodate and iodine ion:
3I2 + 6OH- → 5I- + IO3-+ 3H2O
This is because there is no hypoiodate IO - in the solution. At any temperature, IO- will rapidly undergo its own redox reaction to generate I- and IO3-