Potassium Hydroxide (Caustic Potash): Uses and Hazards Compared with Caustic Soda

Potassium hydroxide (KOH, CAS 1310-58-3), known as caustic potash, is a strong inorganic base very similar in chemistry to sodium hydroxide but based on potassium. It is sold as white flakes, pellets or powder, and as solutions at around 45 to 50 percent. It absorbs moisture rapidly from air, and dissolving it in water releases a large amount of heat.

Main uses

• Liquid and soft soaps, because potassium soaps are softer and more soluble than sodium soaps.
• Alkaline batteries, where a KOH solution is the electrolyte in common zinc-manganese dioxide cells.
• Fertilisers and chemical manufacture, as a source of potassium for potassium phosphates, potassium carbonate and other potassium salts.
• Biodiesel production, as a catalyst for transesterification.
• Food processing: pH control and peeling, with food-grade material (E525).
• Cleaning products, including degreasers and drain openers.
• Analytical chemistry, such as determining the saponification value of fats.

How it differs from sodium hydroxide

Chemically they behave alike, but there are practical differences that matter to a buyer. Potassium hydroxide is more soluble in water and in alcohols, it is generally more expensive, and its salts are often preferred where sodium must be avoided, for example in fertiliser, certain electrolytes and some food applications. Potassium soaps are softer, so they are used for liquid products. When your customer asks for caustic, check which one they mean: the two are not interchangeable in every application, and the molar masses differ, so dosages by weight change.

GHS classification

Potassium hydroxide is classified as harmful if swallowed (acute toxicity category 4, H302), as causing severe skin burns and eye damage (category 1A, H314) and commonly as corrosive to metals (H290). The signal word is Danger and the pictograms are corrosion (GHS05) and exclamation mark (GHS07). As with sodium hydroxide, specific concentration limits determine the classification of dilute solutions, so classify each strength separately.

Handling and safe practice

Wear chemical splash goggles with a face shield, alkali-resistant gloves, an apron and closed footwear. Always add solid slowly to cold water with stirring. Eyewash and safety showers must be available. Caustic burns may not be painful at first, so immediate flushing with large amounts of water for at least 15 minutes is critical, followed by medical attention. Your Section 4 should say so plainly.

Storage

Keep in tightly closed containers of polyethylene or steel, since the solid takes up moisture and carbon dioxide and clumps. Store away from acids, aluminium, zinc, tin, and organic materials such as nitro compounds. Do not use aluminium containers or fittings. Our caustic soda guide and storage compatibility guide explain segregation of bases from acids and reactive metals.

Specification and documents

Typical buyer specifications are assay (for example 90 percent minimum for flakes, with the balance mostly water and potassium carbonate), carbonate, chloride, iron and heavy metals. Liquid grades are sold by concentration and density. For transport, potassium hydroxide solid and solution are Class 8 corrosives with separate entries, so check the current UN numbers. The data we hold on this substance is on the potassium hydroxide page.