# What's the order of oxidising strength of the oxyacids of Chlorine?

What I have been told is that the acidity of the four oxyacids of Chlorine increase in the order $$\ce{HOCl} < \ce{HClO2} < \ce{HClO3} < \ce{HClO4}$$.

I have also been told that the oxidising strength goes in the reverse order. In my knowledge acidic strength should increase with oxidising strength. Where am I going wrong?

For your reference, the Ka values of the acids are as follows:

1. $$\ce{HOCl} = 2.9 \times 10^{-8}$$
2. $$\ce{HClO2} = 1.1 \times 10^{-2}$$
3. $$\ce{HClO3} = 5.0 \times 10^2$$
4. $$\ce{HClO4} = 1 \times 10^3$$
• Don't you mean the oxyacids $\ce{HClO}$, $\ce{HClO2}$, $\ce{HClO3}$, and $\ce{HClO4}$? – Philipp Aug 29 '14 at 12:31

For many acids, the proton $\ce{H+}$ is the oxidizing agent. For example, in the oxidation of zinc with $\ce{HCl}$, the oxidizing agent is $\ce{H+}$.
$$\ce{Zn + 2H+ -> Zn^{2+} + H2}$$
However, for some acids, the conjugate base (anion) is also an oxidant (and usually a more powerful oxidant than $\ce{H+}$. The oxyacids of chlorine are all oxidizing agents through their anions, as is nitric acid and some others:
$$\ce{Zn + 2H+ + 2OCl- -> Zn^{2+} + H2O + 2Cl-}$$
• Formation of $\ce{H2}$ is entropically favorable, but so is conversion of $\ce{2HOCl}$ to $\ce{H2O + 2Cl-}$ (three particles from 2). Additionally, you cannot ignore the contribution to spontaneity from enthalpy. – Ben Norris Aug 30 '14 at 13:25