By Vincent Summers, Updated Mar 24, 2022
Potassium hydroxide (KOH) is a strong base derived from the alkali metal potassium (atomic number 19). It is a key starting material for the synthesis of most potassium salts and has widespread industrial and laboratory applications.
Although not commercially viable due to safety concerns, potassium metal reacts violently with water to produce KOH and hydrogen gas:
2 K + 2 H2O → 2 KOH + H2
The reaction releases a large amount of heat, melting the metal and causing the liberated hydrogen to ignite with a characteristic purple flame. Even a pea‑sized piece of potassium can trigger this explosive behavior.
Early settlers extracted potassium carbonate from wood ash, which can be converted to KOH by heating and subsequent hydration:
K2CO3 → K2O + CO2 (high temperature)
K2O + H2O → 2 KOH
Use a kiln to reach temperatures above 700 °C to drive the decomposition of K2CO3.
Electrolyzing an aqueous KCl solution produces chlorine gas at the anode and KOH at the cathode:
2 KCl + 2 H2O → 2 KOH + Cl2 + H2
Collect the chlorine gas safely or vent it to the atmosphere, and harvest the KOH from the electrolyte.
Potassium hydroxide can also be derived from various potassium salts, though these routes are typically impractical for large‑scale production. For example, potassium azide reacts with water to yield KOH, ammonia, and heat:
2 K3N + 6 H2O → 6 KOH + 2 NH3 + …
Similarly, potassium acetylide and potassium hydride produce KOH along with acetylene and hydrogen gas, respectively.
KOH is highly caustic and can cause severe chemical burns, respiratory irritation, and permanent eye damage. Always consult the Material Safety Data Sheet (MSDS) before handling. Use only trained personnel, and wear full eye protection, chemical‑resistant gloves, and a face shield or goggles. Conduct reactions in a well‑ventilated area or under a fume hood to avoid inhalation of toxic gases.
