ACIDITY OF HYDROGEN HALIDES....
All the hydrogen halides are freely soluble in water and react according to the general equation.......
The steps involved are;(a)the breaking of the hydrogen halogen bond,(b)the hydration of the proton and (c)the hydration of the halide ion. When ..........the energy liberated by the combined hydration energies of the proton and halide ion excessds the bond dissociation energy,step(a)and all three are strong acids in water with acid strength increasing from .........
The bond dissociation energy of the hydrogen fluorine bond in HF is so great that the above equilibrium lies to the left and hydrogen fluoride is a weak acid in dilute aqueous solution. In more concentrated solution,however,a second equilibrium reaction becomes important with the fluoride ion forming the complex ion ....The relevant equilibria are............
or more generally.......
.............
The second equilibrium is displaced to the right as the concentration of hydrogen fluoride is increased and it is found that at a concentration of approximately 5-15M,hydrogen fluoride is effectively a strong acid. In this way hydrogen fluoride differs from all the other hydrogen halides. Anhydrous hydrogen fluoride ionises to a small extent and the following equilibria are establishhed: