Potassium Hydroxide — Frequently Asked Questions

Because the cation determines the physical form of the soap. Potassium salts of fatty acids are soft and highly soluble, giving a paste or a clear liquid, while sodium salts are hard and form a bar. Any liquid or soft soap must therefore be saponified with potassium hydroxide, and no amount of dilution will turn a sodium soap into a true liquid soap.

Because of what happens to the glycerine by-product. Both sodium and potassium methoxide catalyse transesterification effectively, but residual potassium in the crude glycerine makes it saleable as a fertiliser, whereas residual sodium does not and can make the glycerine a disposal problem. That difference in by-product value often outweighs KOH's higher cost.

Because potassium hydroxide solution has substantially higher ionic conductivity than the sodium equivalent, which means lower internal resistance and better performance under load. It also remains liquid at lower temperatures at the concentrations used. Those electrochemical advantages are why alkaline cells are built around KOH despite its cost.

Commonly 90 percent as flakes or pellets, and 45 to 50 percent as a solution. The solid is extremely hygroscopic and must be kept sealed; the solution avoids that handling issue but costs more to freight. As with caustic soda, dissolution is strongly exothermic and the solid must always be added to water, never the reverse.