Potassium bifluoride


Potassium bifluoride is the inorganic compound with the formula KHF2. This colourless salt consists of the potassium cation and the bifluoride anion. The salt is used in etchant for glass. Sodium bifluoride is related and is also of commercial use as an etchant as well as in cleaning products.

Nature of the chemical bond in the bifluoride anion

Potassium bifluoride, as its name indicates, contains a bifluoride, or hydrogen anion: HF2−. This centrosymmetric triatomic anion features the strongest known hydrogen bond, with a F−H length of 114 pm, and a bond energy greater than 155 kJ mol−1.

Synthesis and reactions

The salt was prepared by Edmond Frémy who decomposed it to generate, for the first time, hydrogen fluoride. Potassium bifluoride is prepared by treating potassium carbonate or potassium hydroxide with hydrofluoric acid:
The electrolysis of KHF2 was used by Henri Moissan to isolate the element fluorine in 1886.
A related material containing two equivalents of HF is also known, KH2F3. The industrial production of fluorine entails the electrolysis of molten KH2F3.