Question

In your own words, explain the molecular basis behind a Ka value and how it relates to the underlying strength and stability of the bond to the proton (H+) being dissociated.  In this explanation, do not discuss math or calculation aspects of Ka – focus on bond strength and stability and how changes in that could impact Ka values.

Answer 1

Ka is the quantitative measure of strength of an acid. It is the dissociation constant. Higher the value of Ka higher will be it's acidic strength so if a polar bond is stable and the heterolytic cleavage of H+ ion isn't possible or is difficult then then it's Ka value is small and eventually it's acidic strength is low. So for strong polar acids like HCl the bond stability is very low in aqueous solution as it easily breaks down to H+ and Cl- owing to their high Ka value but for organic acids like acetic acid the removal of H+ is not so easy from a more stable covalently bonded position so it's Ka value is low and acedic strength is also low.