Sodium hydrogen fluoride, NaF,HF

A crystalline primary fluoride is obtained by the action of hydrofluoric acid on sodium fluoride. On heating, it decomposes with elimination of hydrofluoric acid. Its solubility in water increases with rise of temperature. The heat of solution is given by Guntz as -6.2 Cal., and the heat of formation from solid sodium fluoride and gaseous hydrofluoric acid as 17.1 Cal.