Which one of the following orders correctly represents the increasing acid strengths of the given acids?
- HOClO < HOCl < HOClO3 < HOClO2
- HOClO2 < HOClO3 < HOClO < HOCl
- HOClO3 < HOClO2 < HOClO < HOCl
- HOCl < HOClO < HOClO2 < HOClO3
Answer
(4) HOCl < HOClO < HOClO2 < HOClO3
Solution
For oxoacids of the same halogen, acid strength increases with the number of oxygen atoms (oxidation state of Cl: +1, +3, +5, +7).
∵ More O atoms ⇒ greater dispersal of negative charge in the conjugate base (resonance) ⇒ more stable anion ⇒ stronger acid.
Stability of anions: ClO- < ClO2- < ClO3- < ClO4-
∴ HOCl < HOClO < HOClO2 < HOClO3
Answer: (4)