Question

On reacting $Mn{O_2}$ with $HCl$ ,
1. $M{n^{4 + }}$ is reduced to
2. $C{l^ - }$ is oxidised to

A) $M{n^{3 + }},C{l^{4 + }}$
B) $M{n^{2 + }},Cl$
C) $Mn,Cl$
D) $Mn$ is not reduced nor $Cl$ is oxidised

Answer 1

Reaction of $Mn{O_2}$ with $HCl$ is a redox reaction. The reactions in which both oxidation ( loss of electrons) and reduction (gain of electrons) occur simultaneously are termed as redox reactions. First, write the balanced redox reaction of $Mn{O_2}$ with $HCl$, and then find the reduced and oxidised species.

Complete step by step answer:
Redox reaction of $Mn{O_2}$ with $HCl$:
$Mn{O_2} + 4HCl \to MnC{l_2} + 2{H_2}O + C{l_2}$

1.) In the above reaction, $Mn{O_2}$ is converting to $MnC{l_2}$. Now, the oxidation state of $Mn$ in $Mn{O_2}$ is $+ 4$ and the oxidation state of $Mn$ in $MnC{l_2}$ is $+ 2$ . Therefore, $M{n^{ + 4}}$ is changing to $M{n^{ + 2}}$ from going left to right. Since, reduction is the gain of electrons or decrease in the oxidation state of an element, $Mn$ is undergoing reduction in the given reaction. Thus, $M{n^{ + 4}}$ is reduced to $M{n^{ + 2}}$.
Reduction half reaction: $Mn{O_2} + 2{e^ - } \to MnC{l_2}$

2.) On going from left to right in the redox reaction of $Mn{O_2}$ with $HCl$, $HCl$is converted to $C{l_2}$. Oxidation state of chlorine in $HCl$ is $- 1$ while the oxidation state of chlorine in $C{l_2}$ is zero. Since, oxidation is the loss of electrons or increase in the oxidation number of an element, $HCl$ is oxidised here to $C{l_2}$ or we can say, $C{l^ - }$ ion is oxidised to $Cl$.

Oxidation half reaction: $2C{l^ - } \to C{l_2} + 2{e^ - }$
Thus, correct option is B, that is, $M{n^{2 + }},Cl$ because $M{n^{ + 4}}$is reduced to $M{n^{ + 2}}$ and $C{l^ - }$ ion is oxidised to $Cl$ on reacting $Mn{O_2}$ with $HCl$ .
So, the correct answer is “Option B”.

Note: Oxidising agent is an acceptor of electrons while reducing agent is a donor of electrons. In reduction half reaction, manganese is reduced, therefore it acts as an oxidising agent because it accepts electrons. In the oxidation half reaction, chlorine is oxidised and acts as a reducing agent for manganese because it donates electrons to manganese.