Potassium iodide
| Potassium iodide | |
|---|---|
 |
|
| General | |
| Systematic name | Potassium iodide |
| Other names | Kalium
iodide, knollide, potide |
| Molecular formula | KI |
| Molar mass | 166.00 g/mol |
| Appearance | white crystalline solid |
| CAS number | [8781-11-0] |
| Properties | |
| Density and phase | 3.13 g/cm3, solid |
| Solubility in water | 128 g/100 ml (6 °C) |
| Melting point | 680 °C (953 K) |
| Boiling point | 1330 °C (1600 K) |
| Acidity (pKa) | ? |
| Basicity (pKb) | ? |
| Structure | |
| Molecular shape | ? |
| Coordination geometry | ? |
| Crystal structure | ? |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | Slightly hazardous |
| NFPA 704 |
   |
| R/S statement | R: 36, 38, 42-43,
61 S: 26, 36-37, 39, 45 |
| RTECS number | TT2975000 |
| Supplementary data page | |
| Structure & properties | n, εr, etc. |
| Thermodynamic data | Phase
behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions |
potassium
bromide potassium chloride |
| Other cations |
sodium
iodide rubidium iodide calcium iodide |
| Related compounds | ? |
| Except where noted otherwise, data are given
for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references |
|
Potassium iodide is a white crystalline salt with chemical formula K I, used in photography and radiation treatment. It finds widespread application as an iodide source because it is less hygroscopic than sodium iodide, making it easier to work with. KI can turn yellow upon heating in air or upon standing in moist air for long periods, because of oxidation of the iodide to iodine.
Chemical properties
Potassium iodide behaves as a simple ionic salt, K+I-. Since iodide ion is a mild reducing agent, KI is easily oxidised to iodine by oxidising agents such as chlorine:
2 KI( aq) + Cl2( aq) → 2 KCl + I2( aq)
If dichloromethane is present, the purple colour of elemental iodine may be seen in the organic phase. Under acidic conditions, KI is oxidised even more easily, due to the formation of hydroiodic acid (HI), which is a powerful reducing agent.
KI also forms a complex ion I3- when combined with elemental iodine, and in fact this reaction is frequently used to render I2 more soluble in water:
KI( aq) + I2( s) → KI3( aq)
The reaction is slightly reversible, allowing the iodine to be used in aqueous solutions for redox titrations.
Potassium iodide also reacts in some organic reactions as a source of iodide ion (see "uses" below).
Preparation
Potassium iodide may be prepared by the reaction of a potassium base with hydroiodic acid, for example:
HI + KHCO3 → KI + H2O( l) + CO2( g)
Alternatively iron(II) iodide, prepared using scrap iron and iodine (made from iodide rich brines or from Chile saltpeter, can be treated with potassium carbonate:
FeI2 + K2CO3 → 2 KI + FeCO3
Uses
Potassium iodide is used in photography, in the preparation of silver(I) iodide for high speed photographic film:
KI( aq) + AgNO3( aq) → AgI( s) + KNO3( aq)
Potassium iodide is also added to table salt in small quantities to make it "iodized". In a saturated solution, it is also used as an expectorant to treat lung congestion.
KI is often used as a source of iodide ion in organic synthesis. A useful application is in the preparation of aryl iodides from arenediazonium salts[5], for example:
Saturated solution of potassium iodide is also used as treatment for sporotrichosis, a fungal infection.
Role of potassium iodide in radiological emergency preparedness
Potassium iodide may also be used to protect the thyroid from radioactive iodine in the event of an accident or terrorist attack at a nuclear power plant, or other nuclear attack, especially where a nuclear reactor is breached and the volatile radionuclides, which contain significant amount of 131I, are released into the environment. Radioiodine is a particularly dangerous radionuclide because the body concentrates it in the thyroid gland. Potassium iodide cannot protect against other causes of radiation poisoning, however, nor can it provide any degree of protection against a dirty bomb unless the bomb happens to contain a significant amount of radioactive iodine.
The purpose of radiological emergency preparedness is to protect people from the effects of radiation exposure after an accident at a nuclear power plant. Evacuation is the most effective protective measure in the event of a radiological emergency because it protects the whole body (including the thyroid gland and other organs) from all radionuclides and all exposure pathways. However, in situations when evacuation is not feasible and in-place sheltering is substituted as an effective protective action, administering potassium iodide reduces the effects of radio iodine by 99%, and is a prudent, inexpensive supplement to sheltering. Potassium iodide protects the thyroid gland against internal uptake of radioiodines that may be released in the event of a nuclear reactor accident or from fallout. When potassium iodide is ingested, it is taken up by the thyroid gland. In the proper dosage, and taken at the appropriate time, it will effectively saturate the thyroid gland in such a way that inhaled or ingested radioactive iodines will not be accumulated in the thyroid gland. The risk of thyroid effects is reduced. Such thyroid effects resulting from radioiodine uptakes due to inhalation or ingestion, or both, could result in acute, chronic, and delayed effects. Acute effects from high doses include thyroiditis, while chronic and delayed effects include hypothyroidism, thyroid nodules, and thyroid cancer. The FDA has approved potassium iodide as an over-the-counter medication. As with any medication, individuals should check with their doctor or pharmacist before using it.
A low-cost alternative to commercially available iodine pills is a saturated solution of potassium iodide. It usually possible to obtain several thousand doses for prices near US$ 0.01/dose. Long term storage of KI is normally in the form of reagent grade crystals, which are convenient and available commercially. The purity is superior to "pharmacologic grade". Its concentration depends only on temperature, which is easy to determine, and the required dose is easily administered by measuring the required volume of the liquid. At room temperature, the U.S. standard adult radiological protective dose of 130mg is four drops of a saturated solution. A baby's dose is 65mg, or two drops. It's normally administered in a ball of bread, because it tastes incredibly bad. Use is contraindicated in individual known to be allergic to iodine. (see chap 13, Kearney, below)
Precautions
Irritant. Wear gloves and goggles. Chronic oxerexposure can have adverse effects on the thyroid.
Suppliers/Manufacturers
- VWR
- Strem
- Alfa
- Sigma-Aldrich
- Fisher
- Iosat-ThyroShield Potassium Iodide