Why Hydrochloric acid (HCl) is stronger acid than hydroflouric acid (HF) ?

 

Here first of all recall the definition of an acid.According to Arrhenius concept,

Acid is a species which can produce protons (H⁺⁾  in its aqueous solution.

Now its easy to understand that which species gives more protons will be more strong acid. Hydrogen flouride (HF) is having strong hydrogen bonding , as fluorine is highly electronegative atom and offers strong  Hydrogen bonding. Due to this hydrogen bonding , hydrogen is tightly trapped between two highly electronegative F atoms. Such entrapped H⁺are difficult to be free.

On the other hand HCl molecule is having dipole- dipole intermolecular force which is weaker than hydrogen bonding so H⁺entrapped between two Cl atoms are easy to get free.

Hence these are the type of intermolecular forces - hydrogen bonding in HF and simple dipole -dipole forces in HCl - which are making HCl stronger acid than HF.