Question

Give a brief account of the acidic nature of the oxoacids of chlorine.

Answer 1

1. Chlorine forms four oxoacids: hypochlorous (HOCl), chlorous (HClO₂), chloric (HClO₃), and perchloric acid (HClO₄).
2. Acid strength increases with the oxidation state of chlorine or the number of oxygen atoms: HOCl < HClO₂ < HClO₃ < HClO₄.
3. This is because more oxygen atoms stabilise the conjugate base (anion) by dispersing the negative charge through resonance.
4. The greater the stability of the anion formed after losing a proton, the stronger the acid.
5. For the same oxidation state, acid strength decreases with increasing atomic number of the halogen (Cl > Br > I).
6. The \[\ce{H - O}\] bond polarity influences acidity; a more polar \[\ce{H - O}\] bond breaks easily to release H⁺, making the acid stronger.
7. Thus, perchloric acid (HClO₄) is the strongest acid among the chlorine oxoacids due to the highest oxidation state and anion stability.