Potassium iodide

Potassium iodide (KI) is a salt of hydroiodic acid. In appearance it is a solid, colorless crystalline substance with crystals of cubic form. Potassium iodide in air with heating or under the influence of light turns yellow due to the oxygen oxidation of iodine ions to elemental iodine. As the temperature increases, the solubility of the salt in the water increases. In 128 g of water, 128 g of salt are dissolved at 0 ° C, 145 g at 20 ° C, 176 g at 60 ° C, 209 g at 100 ° C. The molar mass of the compound is 166.00277 g / mol. The refractive index is equal to 1.667. The density is 3.13 g / cm³. The melting point is 686 ° C. The boiling point is 1330 ° C. Potassium iodide is less hygroscopic (it absorbs water less readily) than sodium iodide, so it is easier to work with it.

Potassium iodide is a soft reducing agent, it is easily oxidized by chlorine: 2KI + Cl2 → 2KCl + I2. Reacts with iodine, resulting in a Lugol solution: KI + I2 → KI3. The potassium salt of hydroiodic acid can be obtained by reacting iodine with potassium hydroxide 6KOH + 3I2 = 5KI + KIO3 + 3H2O or by reducing potassium iodate with carbon 2KIO3 + 3C = 2KI + 3CO2. The yellow color of salt with expired shelf life indicates the oxidation of iodide to iodine according to the reaction equation: 4KI + 2CO2 + O2 → 2K2CO3 + 2I2.

In nature, iodine is present everywhere, but is considered a rare element, so its content in all natural sources is insignificant. Like other halogens characterized by high reactivity, it is usually found in the form of compounds, namely sodium and potassium alkali iodides, but (in contrast to other halogens) also in the form of iodates dissolved in water. However, it never exists, as iodine nitrogen (IN3), since it is a very unstable and rapidly decomposing compound with an explosion. In the waters of the ocean or from underground sources, iodides and iodates are contained, approximately, in equal amounts. Since potassium iodide is soluble in water, iodine ions are present in the ocean, seaweed and marine fish. Seafood is the main source of human iodine intake, since they contain many times more iodine compounds than in living creatures that live on land. And the main raw material for industrial production of iodine is drilling water or some types of algae.

Potassium iodide contained in drilling water is used in the industry to produce iodine: KI + Cl2 → KCl2 + I2. It is also widely used as a source of iodide ions. In analytical chemistry, potassium iodide is used for oxidation-reduction iodometric titration. Paper moistened with a solution of salt and starch, helps to qualitatively determine the presence of chlorine, ozone or other oxidants in the presence of which the combined iodine is released, and the starch applied to the paper turns blue. Used as a food additive in animal feed, as well as in human nutrition: in small amounts, for the prevention of the development of endemic (enlargement of the thyroid) diseases, which are often found in a number of geographical areas due to natural iodine deficiency, potassium iodide, along with Potassium iodate, added to table salt. The food product obtained in this way is called iodinated salt. The warranty period of storage of such salt is limited, because over time, under the influence of excess oxygen and carbon dioxide, KI is slowly oxidized to metal carbonate and elemental iodine, which then evaporates.

In medicine potassium iodide is used as a medicine. Potassium iodide is available in various dosage forms: tablets, oral solution, film-coated tablets, eye drops, chewable tablets. Drugs repair iodine deficiency in the body, have antithyroid (they inhibit the biosynthesis of hormones in the thyroid gland), mucolytic (thin in the lungs and facilitate its release), expectorant, antifungal, absorbable, radioprotective (protects the thyroid from radiation and prevents the absorption of radioactive iodine ) Action. The recommended dosage of WHO in the event of emergencies involving radioactive iodine depends on the age and is:

• For people over 12 years - 130 mg per day;
• From 3 to 12 years - 65 mg per day;
• At the age of 1 to 36 months - 32 mg per day;
• Children younger than 1 month - 16 mg per day.

WHO does not recommend taking iodine for people over 40 years of age for prevention of potassium.