What is Potassium Iodide?

by Lucy Bell-Young

Potassium iodide (KI) is an inorganic chemical compound that serves many purposes. Continue reading to find out more about KI.

How is Potassium Iodide Made?

Potassium iodide can be produced using several different methods, but it is most popularly obtained by reacting elemental iodine (I) with a hot, concentrated solution of potassium hydroxide (KOH). Here’s how it works:

  1. Adding the KOH to Water: it starts when potassium hydroxide is added to a beaker of water. This will have an exothermic reaction and generate a lot of heat.
  2. Adding the Elemental Iodine: the solution must be hot when adding elemental iodine, otherwise the reaction will take longer and may not go through to completion.
  3. Colour Change: as soon as the elemental iodine is added, the solution will begin turning a yellowish colour. This will eventually dissolve away as all the iodine is used up.
  4. Potassium Iodate: once everything has dissolved, precipitates of potassium iodate (KIO3) will begin forming at the bottom of the solution.
  5. Filtering: unlike potassium iodide, KIO3 is insoluble in water and can be separated easily. Once the solution has cooled down, it is filtered to remove any precipitates.
  6. Boiling it Down: the solution of potassium iodide is then boiled down in order for it to crystallise. When this happens, KI takes its form as a white, salt-like solid.


Because it is composed of a metal (potassium) and halogen (iodine), KI is classed as a metal halide. Here are some of its other notable properties:

  • It is extremely soluble with a range of solvents like water, alcohol, acetone and glycerol
  • It is hygroscopic in moist air and slightly deliquescent in dry air
  • Long exposure to air causes potassium iodide to oxidise and turn yellow
  • It has a boiling point of 1323°C
  • It has a melting point of 681°C
  • It can dissolve elemental iodine
  • It has a neutral to slightly alkaline pH

Chemically, its properties make it well-suited to a range of uses. For example, potassium iodide absorbs water less readily than its relative sodium iodide and is, therefore, easier to work with.

Large glass jars of glycerin on a table
Potassium iodide is soluble in a variety of solvents including water, alcohol, acetone and glycerine. This makes it easy to work with.

What is KI Used For?

Potassium iodide has a variety of uses and has found its place in the food, medical and even cosmetic industry. We’ll look at its uses in more detail next week, but for now here’s a summary of what potassium iodide is widely used for:

  • Dietary Supplement: potassium iodide is commonly used to iodise table salt and can even be used in animal feeds. This is because of the health benefits it possesses.
  • Thyroid Protectant: KI is sold in tablets which could prove vital in the case of a nuclear accident. Potassium iodide can actually block the thyroid from absorbing any radioactive iodine, ensuring that your thyroid is protected against cancer-causing radiation.
  • Expectorant: in the medical field, potassium iodide is commonly used to treat long-term breathing conditions, like asthma, because it is able to decrease mucus viscosity.
  • Fluorescent Quenching Agent: interestingly, specific types of KI solutions are able to influence the intensity of fluorescence in various products.

In chemistry, there are a variety of experiments and reactions that involve potassium iodide:

  • Silver Iodide (AgI): potassium iodide is used in combination with silver nitrate (AgNO3) to produce silver iodide, a compound that is used in photographic film
  • Elephant’s Toothpaste: potassium iodide is used to catalyse the decomposition of hydrogen peroxide, a reaction that produces a violent eruption of thick foam
  • Organic Synthesis: KI popularly used in the Sandermeyer reaction, where it converts arylamines into aryl iodides

Safety Hazards

Although it can be used in the medical industry and is “generally recognised as safe” as a product in food, potassium iodide can be toxic if chronically consumed.

Symptoms of the toxicity of KI include:

  • A metallic taste in the mouth
  • Swollen eyes
  • Vomiting
  • Gastric pain
  • Diarrhoea
  • Oedema of the throat
Nuclear plant
Potassium iodide is used in tablets that are aimed at protecting your thyroid against radioactive iodine following a nuclear accident. Photo by Bedrijfsfotograaf Fredography


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