Potassium hydroxide (KOH) is an odourless, white or yellow inorganic compound that’s usually in flaky or lumpy solid form at room temperature.
It’s often used to make liquid soap, although KOH has many other household and industrial applications too. For example, it’s a common component in liquid drain cleaners and paint and varnish removers. Potassium hydroxide is also used as an electrolyte in alkaline batteries and in lithography and electroplating.
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What is potassium hydroxide?
Potassium hydroxide is classified as an inorganic strong base because it completely dissociates into metal ions and hydroxide ions when dissolved in water. It has the chemical formula KOH, which has a strong ionic bond between an alkali metal and hydroxide group.
Much like sodium hydroxide, potassium hydroxide is known for its wide variety of uses. In fact, it’s estimated that around 800,000 metric tonnes of potassium hydroxide are produced every year. Furthermore, the global market for this chemical is estimated to grow to $2.79 billion by 2027.
The global production of potassium hydroxide is primarily used to manufacture potassium carbonate (K2CO3), as shown in the balanced chemical equation below.
CO2 + 2KOH → K2CO3 + H2O
The reaction between carbon dioxide and potassium hydroxide produces potassium carbonate and water. In turn, the potassium carbonate serves as a feedstock in synthesising various organic and inorganic chemical products, including fertilisers intended for acidic soil. It’s also used as a raw material for condensation agents and drying neutralisation.
Is potassium hydroxide dangerous?
Potassium hydroxide is extremely caustic, especially at high concentrations. On contact, it can irritate or burn the skin and even damage the mucous membranes. Here are some of the main hazards associated with potassium hydroxide:
- Toxic when inhaled or ingested
- Can irritate the nose and throat
- May cause headaches and dizziness
- Can damage the eyes and cause blindness
- If inhaled, it can irritate the lungs and cause a build-up of fluid (pulmonary oedema)
It’s important to take extra precautions when handling solid or highly-concentrated potassium hydroxide solutions in the laboratory. You must avoid getting into direct contact with it and you always wear goggles, gloves and personal protective clothing such as a lab gown or apron. It’s also advisable to wear gloves if you’re using a low concentration solution of potassium hydroxide as a cleaning agent. 
And, of course, you’ll need to be aware of the relevant first aid remedies in case you come into contact with potassium hydroxide, whether on the skin, in the eyes or through inhalation or ingestion.
Is potassium hydroxide an acid?
Potassium hydroxide is not an acid; it’s actually the opposite, which is a base or alkaline. However, in pure solid anhydrous form, potassium hydroxide is technically a salt because of its ionic bonds and crystalline structure.
In this form, it’s neither an acid nor a base. It only becomes a base or alkaline solution when it absorbs moisture or is dissolved in water.
An aqueous solution of potassium hydroxide is classified as a base for several reasons:
- It has a pH level above 7 (neutral), which can turn red litmus paper blue
- The ions completely dissociate into metallic ions and hydroxyl ions
- It has a dissociation constant (Kb) of 3.16 X 10-1
- It becomes a proton acceptor, which makes it a base according to the Brønsted-Lowry definition
Is potassium hydroxide a strong base?
Yes, potassium hydroxide is a strong base. Strong bases are defined by their ability to completely dissociate into cations and hydroxyl ions (-OH) in an aqueous solution. They also tend to be monoprotic bases, which means they only accept one proton per molecule.
Another indication of a base’s strength is its dissociation constant, which in this case is (Kb) of 3.16 X 10-1.
What is the use of potassium hydroxide?
Here are some of the most common applications of potassium hydroxide:
- Liquid soaps – many liquid soaps are made from potassium hydroxide. They tend to be softer than those made from sodium hydroxide and require less water to be dissolved. That means they can easily be converted into liquid form.
- Food processing – potassium hydroxide is used in the food industry as a thickening agent, to control pH levels, and as a food stabiliser.
- A precursor to other potassium compounds – many inorganic and organic potassium salts are prepared through the neutralisation reactions of potassium hydroxide with acids. Some of the more common salts that are produced in this way include carbonate, cyanide, permanganate, phosphate, and various silicates. Potassium phosphate, which is used as an ingredient in fertilisers and explosives, is one such example.
- Battery electrolyte – many types of rechargeable alkaline batteries use an aqueous solution of potassium hydroxide as an electrolyte because it’s more conductive than sodium hydroxide. This is especially true for batteries that are based on nickel-cadmium, nickel-hydrogen, and manganese dioxide-zinc.
- Chemical cremation – as potassium hydroxide is highly caustic, it can easily dissolve organic tissue. It’s therefore used in the resomation (alkaline hydrolysis) or chemical cremation of human remains. It can also be used in entomology to dissolve soft insect tissue and reveal the finer details of exoskeletons.
- Hair removal – potassium hydroxide can be an effective means of removing hair from animal hides during the tanning process.
When it comes to its chemical and physical properties, potassium hydroxide is almost identical to sodium hydroxide. It’s perhaps no surprise then that their applications are virtually interchangeable. One notable difference is that sodium hydroxide is preferred for large-scale industrial applications because it’s more affordable.
What type of substance will neutralise the potassium hydroxide solution?
Being a strong base means potassium hydroxide is easily neutralised by any strong acid. As a monoprotic base, it can also be neutralised by higher concentrations of weak acids. These neutralisation reactions produce potassium salts. The example below shows how nitric acid can easily neutralise potassium hydroxide:
HNO3 + KOH → H2O + KNO3
What is the difference between sodium hydroxide and potassium hydroxide?
Sodium and potassium belong to the same alkali metals group in the periodic table. As such, both are highly reactive elements that cannot be found naturally in elemental form.
The main difference between them is their relative reactivity. Potassium is more reactive than sodium and is also a much stronger base.
