What is Potassium Hydroxide?

by

Kate Onissiphorou

Potassium hydroxide (KOH) – which you might also hear called caustic potash or lye – is an inorganic compound. Just like other strong bases, it’s highly caustic and completely dissociates into ions when dissolved in water.

The other seven strong bases include:

• LiOH (lithium hydroxide)

• NaOH (sodium hydroxide)

• Ca(OH)2 (calcium hydroxide)

• CsOH (caesium hydroxide)

• Sr(OH)2 (strontium hydroxide)

• RbOH (rubidium hydroxide)

• Ba(OH)2 (barium hydroxide).

Potassium hydroxide is sold in various forms including pellets, powders, and flakes. It also has several industrial applications, such as in the manufacture of soft soaps.

Potassium hydroxide is interchangeable with sodium hydroxide, although it’s less widely used in industrial applications because it’s more expensive.

How is potassium hydroxide made?

Potassium hydroxide occurs naturally through the leaching process from wood ashes that are burned in forest fires caused by lightning or the auto-ignition of dried leaves. Ancient people learned how to make soaps through the leaching process by intentionally burning wood, extracting hydroxide compounds from the ashes and then adding water to filter out the particles.

However, the leaching process is not an efficient way of producing potassium hydroxide on a large scale. Just like many other synthetic chemical manufacturing methods, the industrial production of potassium hydroxide uses cheap and readily available feedstocks.

Traditionally, potassium hydroxide was manufactured from the reaction between potassium carbonate and calcium hydroxide solutions. Solid calcium carbonate forms a solid precipitate, while the water-soluble potassium hydroxide remains in the aqueous solution.

Ca(OH)2 + K2CO3 → CaCO3 + 2 KOH

The solid calcium carbonate precipitate is filtered out and the remaining solution of potassium hydroxide is then boiled down, leaving behind a solid crystalline potassium hydroxide. However, this manufacturing technique is now an outdated method and was discontinued in the late 19th century.

Today, potassium hydroxide is mass-produced through the electrolysis process. A solution of potassium chloride is subjected to a steady direct current, thereby removing the chlorine gas and hydrogen gas. This allows the potassium to react with hydroxide from the water.

2 KCl + 2 H2O → 2 KOH + Cl2 + H2

The hydrogen gas is released from the cathode side, while the chlorine gas is released from the anode side.

Approximately 800,000 metric tonnes of potassium hydroxide are produced each year using this method, with the total global market value estimated to grow to $2.79 billion by the year 2027.

Chemical Formula of Potassium Hydroxide

The chemical formula of potassium hydroxide is KOH. The compound has an ionic bond, which means the molecule exhibits polarity. The hydroxide side is negatively charged while the potassium side is positively charged, as shown in the illustration below.

What is potassium hydroxide used for in everyday life?

Potassium hydroxide has several industrial and commercial applications, some of which are analogous to those of sodium hydroxide, such as in manufacturing soaps. A few of the main uses of potassium hydroxide are summarised below.

1. Manufacturing dyes
   Certain dyes like methylene blue and congo red require their molecules to be activated by potassium hydroxide. This is the case for the carbons of dye molecules such as resorcinol-formaldehyde carbon gels, for example.
2. Batteries
   Some alkaline batteries use potassium hydroxide as an electrolyte because it’s a better conductor than other hydroxides, such as sodium hydroxide.
3. Chemical precursor
   Potassium hydroxide is used as a precursor in the manufacture of some potassium compounds such as fertilisers. Potassium salts of carbonate, cyanide, permanganate, phosphate, and silicates can also be prepared using potassium hydroxide.
4. Chemical cleaning products
   Similar to sodium hydroxide, potassium hydroxide can be used in the saponification of fats to create soaps, detergents, and other cleaning products. Even potassium hydroxide solution alone makes an effective cleaning agent that’s capable of removing greasy organic compounds.

Is potassium hydroxide safe?

All caustic hydroxide compounds are dangerous and can cause severe burns and other tissue damage. They’re also poisonous when ingested, especially in high concentrations. Potassium hydroxide is no exception. It is a highly corrosive and caustic compound that can dissolve organic substances, including living tissue.

It’s therefore vital to handle potassium hydroxide safely and ensure its stored correctly. You must wear the appropriate protective clothing, goggles, and gloves when handling potassium hydroxide or any other caustic substance. If your skin comes into contact with it, rinse the area thoroughly with water. You should always refer to the safety data sheet to check the proper protocols for handling, using, and disposing of potassium hydroxide.

In terms of whether potassium hydroxide is safe for the environment, it’s unusual for large amounts to find its way into water sources. When it does, the pH of the water will significantly increase, typically only for a short time, and this can be toxic to local wildlife. Read our article to find out more about whether potassium hydroxide is harmful to the environment.

Where to buy potassium hydroxide

Depending on the quantity and quality of potassium hydroxide that you need, you may be able to search for suppliers in your local area. The cost tends to be lower for bulk orders. You can also shop for potassium hydroxide online, but it’s best to only buy such products from trusted chemical suppliers and manufacturers.

Disclaimer

The blog on chemicals.co.uk and everything published on it is provided as an information resource only. The blog, its authors and affiliates accept no responsibility for any accident, injury or damage caused in part or directly from following the information provided on this website. We do not recommend using any chemical without first consulting the Material Safety Data Sheet which can be obtained from the manufacturer and following the safety advice and precautions on the product label. If you are in any doubt about health and safety issues please consult the Health & Safety Executive (HSE).