$\huge \sf Redox~Reactions$

Question

abhisar · Answer

$\large \sf Classical~Idea~Of~Reduction~and~Oxidation$

abhisar · Answer

$\bullet$ Oxidation is defined as the addition of Oxygen/electronegative element to a substance or removal of Hydrogen/electropositive element from a substance.

$\bullet$ Reduction is defined as removal of Oxygen/electronegative element from a substance or addition of Hydrogen/electropositive element to a substance.

$\bullet$ Oxidation and reduction always occur simultaneously and hence, the word $\bf Redox$ is used to describe this class of chemical reaction.

Examples:

$\sf H_2S+Cl_2\rightarrow2HCl+S$
Here, $\sf H_2S$ is oxidised due to the addition of electronegative element Cl and $\sf Cl_2$ is reduced due to the addition of Hydrogen.

abhisar · Answer

$\sf \large Redox~reaction~in~terms~of~Electron~Transfer$

$\bullet$ In a redox reaction, the half reaction that involves loss of electrons are called as Oxidation reaction.

$\bullet$ In a redox reaction, the half reaction that involves gain of electrons are called as Reduction reaction.

$\bullet$ The species which loses electron is called as $\bf Reducing~agent$ and the species which gains electron is called as $\bf Oxidizing~agent$.

Example:
$\sf 2Na+H_2\rightarrow 2NaH$

Half reactions
$\sf 2Na\rightarrow 2Na^+2e^-$       $\bf [Oxidation]$
$\sf H_2+2e^- \rightarrow 2H^-$      $\bf [Reduction]$

abhisar · Answer

$\sf \large Oxidation~Number$
Oxidation number denotes the oxidation state of an element in a compound ascertained accordingto a set of rules formulated on the basis that electron in s Covalent bond belongs entirely to more electronegative element.

$\bf Rules$
$\bullet$ Elements in the free and uncombined state bears an oxidation number of Zero. Example: Oxidation number of Ag, O, H, S and P in Ag, $\sf O_2,H_2,S_8~and~P_4$ is 0

$\bullet$ For ions composed of only one atom, the oxidation number is equal to the charge on ion.

$\bullet$ Oxidation number of oxygen is -2 in most of the cases but there are few exceptions.
       i) In peroxides and superoxides
             a) In peroxide, oxidation number of O is -1
             b) In superoxides like $\sf KO_2, RbO_2$, oxidation number
                 of each O atom is -1/2
        ii) In compunds with fluorine, oxidation number of oxygen is positive.
            For example, in $\sf OF_2$ it's +2 and in $\sf O_2F_2$ it's +1

$\bullet$ Oxidation number of Hydrogen is +1. But in metal hydrides like LiH, NaH etc, it's -1

$\bullet$ Oxidation number of Fluorine is always -1. Other halogens also have an oxidation number of -1. Chlorine, iodine and Bromine when combined with oxygen, for example in oxoacids and xoanions, have +ve oxidation  numbers