Question

Justify giving reactions that among halogens, fluorine is the best oxidant and among other hydrohalic compounds, hydroiodic acid is the best reductant.

Answer 1

Oxidants also means oxidising agent which oxidises others and reduces itself. Fluorine has the maximum standard reduction electrode potential than the other halogens.

Complete step by step solution:
Reduction occurs when any species gains electrons and oxidation occurs when any species loses electrons. Oxidation can also be termed as the addition of oxygen or removal of hydrogen from any species. Reduction can be termed as the addition of hydrogen or removal of oxygen from any species. The increase in oxidation number is termed as oxidation and decrease in oxidation number is termed as the reduction.
Fluorine exists as the diatomic gas molecule. Fluorine acts as an oxidising agent or oxidant. It oxidises all the halo ions such as chloride, bromide and iodide as follow:
${{\text{F}}_2} + 2{\text{C}}{{\text{l}}^ - } \to 2{{\text{F}}^ - } + {\text{C}}{{\text{l}}_2}$
${{\text{F}}_2} + 2{\text{B}}{{\text{r}}^ - } \to 2{{\text{F}}^ - } + {\text{B}}{{\text{r}}_2}$
And with iodine,
${{\text{F}}_2} + 2{{\text{I}}^ - } \to 2{{\text{F}}^ - } + {{\text{I}}_2}$
Fluorine gains electrons and turns into anion.
In the same way chlorine can reduce the lower anion such as bromide and iodide and bromine can reduce iodide. But the reverse does not happen like the bromide, iodide and chloride cannot oxidise the fluorine or higher halogens.
The hydroiodic acid acts as a very good reducing agent. It reduces other compounds and reduces itself. When we reacts hydroiodic acid with the sulphuric acid then iodine and sulphur dioxide forms the reaction occurs as follow:
${\text{HI}} + {{\text{H}}_2}{\text{S}}{{\text{O}}_4} \to {{\text{I}}_2} + {\text{S}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}$
As we can see that the oxidation state of iodide in acid increases from minus 1 to zero

Hence, oxidation is occurring.

Note: The electrode potential represents the tendency of any species to lose or gain electrons when it is placed in the solution of its own ion. The standard potential represents standard reduction potential at standard condition of temperature and pressure calculated using standard hydrogen electrode.