Question

In the following reactions:
a. $3Mn{O}_2+4Al⟶3Mn+2{Al}_2{O}_3$
b. $2Mn{O}_4^{\ominus }+16H^{\oplus }+10{Cl}^{\ominus }⟶2{Mn}^{2+}+5{Cl}_2+8H_{2}O$
Which species is reduced and which is oxidised?

• A. a. $Mn{O}_2$ is reduced and aluminium is oxidised. b. $Mn{O}_4^{\ominus }$ is reduced, and ${Cl}^{\ominus }$ is oxidised.
• B. a. $Mn{O}_2$ is oxidised and aluminium is reduced. b. $Mn{O}_4^{\ominus }$ is reduced, and ${Cl}^{\ominus }$ is oxidised.
• C. a. $Mn{O}_2$ is reduced and aluminium is oxidised. b. $Mn{O}_4^{\ominus }$ is oxidised, and ${Cl}^{\ominus }$ is reduced.
• D. None of these

Answer 1

The correct option is A a. $Mn{O}_2$ is reduced and aluminium is oxidised. b. $Mn{O}_4^{\ominus }$ is reduced, and ${Cl}^{\ominus }$ is oxidised.

a. $3Mn{O}_2+4Al⟶3Mn+2{Al}_2{O}_3$
The oxidation number of Al increases from 0 to +3 and the oxidation number of Mn decreases from +4 to 0.
$Mn{O}_2$ is reduced and aluminium is oxidised.
b. $2Mn{O}_4^{\ominus }+16H^{\oplus }+10{Cl}^{\ominus }⟶2{Mn}^{2+}+5{Cl}_2+8H_{2}O$
The oxidation number of Cl increases from -1 to 0 and the oxidation number of Mn decreases from +7 to +2.
$Mn{O}_4^{\ominus }$ is reduced and ${Cl}^{\ominus }$ is oxidised.