Potassium bifluoride

Potassium bifluoride is the inorganic compound with the formula K[HF2]. This colourless salt consists of the potassium cation (K+) and the bifluoride anion ([HF2]-). The salt is used as an etchant for glass. Sodium bifluoride is related and is also of commercial use as an etchant as well as in cleaning products.

Synthesis and reactions
The salt was prepared by Edmond Frémy by treating potassium carbonate or potassium hydroxide with hydrofluoric acid:
 * 2 HF + KOH → K[HF2] + H2O

With one more equivalent of HF, K[H2F3] (CAS#12178-06-2, m.p. 71.7 C) is produced:
 * HF + K[HF2] → K[H2F3]

Thermal decomposition of K[HF2] gives hydrogen fluoride:
 * K[HF2] → HF + KF

Applications
The industrial production of fluorine entails the electrolysis of molten K[HF2] and K[H2F3]. The electrolysis of K[HF2] was first used by Henri Moissan in 1886.