Great question - a lot of my students have asked me similar ones in the past. Whenever you want to decide whether or not an acid is strong (or more generally, whether a certain reaction is favorable) you have to take into account both the forward and reverse reactions. Ideally, you want a favorable forward reaction and an unfavorable reverse reaction. In other words, you want your products to be so stable that they're unlikely to change back to your reactants. The classic example of this is the difference between HF and HI in terms of acidity. While F is indeed much more electronegative than I, and therefore loses a proton fairly easily, due to F's small atomic radius, it is unstable in solution and likes to attack the H+ to form HF again. I-, on the other hand is stable in solution. So, after HI dissociates, they remain separate and therefore the products are stable...rxn is favorable. That's why HF is a weak acid while HI is very, very strong.
This is the same case here. ClO- isn't that stable in solution. O isn't really happy hanging around with a -1 charge for the same reason F isn't either. In these cases, stability of products trumps the electronegativity difference that allows the reaction to proceed in the first place.[/QUOTE
Thank you! This makes sense. So is safe to say that this occurs with most compounds containing O in relation to acidity?
