HF or hydrogen fluoride is also called hydrofluoric acid. It is composed of the proton cation (H+) and the fluoride anion (F-). Fluorine is the most electronegative element on the periodic table and as such readily forms the fluoride anion. Such a large degree in electronegativity difference between fluorine and hydrogen guarantees that the bond between then will be ionic. A simple chemical test to prove the acidity of HF would be to add some HF to an aqueous solution of sodium bicarbonate (NaHCO3). Sodium bicarbonate is a mild base and reacts with acids to produce carbonic acid (H2CO3) which breaks down into water and carbon dioxide. So when you add HF to NaHCO3, you will see the carbon dioxide bubble out of solution, thus proving the acidity of HF.