Potassium hydroxide (KOH) — properties, uses, production and safety

Characteristics and chemical behavior

KOH is a white, crystalline solid that is highly soluble in water; dissolution is exothermic and the solid is hygroscopic and deliquescent, absorbing moisture and carbon dioxide from the air. The active species in solution is the potassium ion paired with the hydroxide ion, which is responsible for high pH and strong corrosivity. It reacts with acids to produce salts and water and can attack many metals, releasing hydrogen gas. For additional technical details see compound data.

Origin and industrial production

Historically, alkaline solutions derived from wood ashes (potash) were the earliest source of potassium compounds and lye. The modern chemical potassium was isolated in the early 19th century, and industrial KOH is now produced mainly by electrolysis of potassium chloride solutions, a chloralkali-type process analogous to sodium hydroxide manufacture. Other laboratory routes include neutralization of potassium carbonate with calcium hydroxide.

Main uses and examples

• Manufacture of liquid soaps and soft cleansers: potassium soaps remain more soluble than sodium soaps, making KOH preferred for liquid formulations.
• As a strong base and catalyst in organic synthesis and laboratory titrations.
• Electrolyte in some types of alkaline batteries and in certain fuel cell and electrochemical applications.
• In biodiesel production, pH adjustment, metal cleaning and as a precursor to potassium salts and fertilizers.

Handling, hazards and comparisons

KOH is corrosive to skin, eyes and mucous membranes; appropriate personal protective equipment (gloves, goggles, lab coat) and ventilation are recommended. Contact with acids or water can liberate heat; contact with some metals generates flammable hydrogen. Compared with sodium hydroxide (NaOH), potassium hydroxide often yields more soluble potassium salts and is favored where liquid products or specific potassium salts are required. Dispose of residues in accordance with local regulations and avoid release to the environment.