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I have seen various different contradicting statements about oxoacids of chlorine regarding oxidising strength & reducing strength of these.

I understand the trend for acidity that HClO4 is strongest and HClO is weakest , but what about oxidisind and reducing character,

Some day that HClO4 is strong reducing as well as strongest oxidising agent as well,

I understand that it will perform reduction of itself and oxidise other element but what about reducing strength?

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    $\begingroup$ Some say that lion's bites heal wounds. $\endgroup$ Apr 4, 2019 at 15:42
  • $\begingroup$ Yeah, saying that HClO4 is strong reducing agent makes as much sense as what Ivan mentions. $\endgroup$
    – Mithoron
    Apr 4, 2019 at 22:00

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When you are considering redox reactions, you should get familiar with electrochemical series (Ref.1). Oxidizing and reducing characters of certain reagent also depends on the conditions used as well. For example, according to Ref.1, $\ce{HClO}$ in acidic medium: $$\ce{HClO + H+ + e- <=> 1/2Cl2 + H2O} ~~~~~~~~ \mathrm{E}^\circ = \pu{+1.594 V} $$ On the other hand, $\ce{ClO-}$ in basic or neutral medium: $$\ce{ClO- + H2O + 2e- <=> Cl- + 2OH-} ~~~~~~~~ \mathrm{E}^\circ = \pu{+0.890 V} $$

Consider the following half reaction: $$\ce{Br2 + 2e- <=> Br- } ~~~~~~~~ \mathrm{E}^\circ = \pu{+1.098 V} $$

Now, you can say that $\ce{HClO}$ in acidic medium spontaneously oxidizes $\ce{Br-}$ to $\ce{Br2}$, but $\ce{ClO-}$ in basic or neutral medium cannot spontaneously oxidize $\ce{Br-}$ to $\ce{Br2}$.

In similar way, you may also say that $\ce{HClO}$ in acidic medium is a better oxidizing agent than that of $\ce{ClO4-}$ in acidic medium, because: $$\ce{ClO4- + 8H+ + 7e- <=> 1/2Cl2 + 4H2O} ~~~~~~~~ \mathrm{E}^\circ = \pu{+1.392 V} $$


Reference:

  1. Steven G. Bratsch, “Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K,” Journal of Physical and Chemical Reference Data 1989, 18(1), 1–21 (https://doi.org/10.1063/1.555839).
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