Identify whether each of the following reaction is a redox reaction. If it is so, by showing the change in oxidation numbers identify the oxidizing agent and reducing agent.

 

4 CaSO₃ ? 3 CaSO₄ + CaS

 

2 KMnO₄+ 3 H₂O₂ → 2 MnO₂ + 2 KOH + 2 H₂O + 3 O₂

 

Both the reactions are redox reactions.

1] CaSO43 acts as both oxidizing and reducing agent.

2] KMnO4 acts as both oxidizing agent.

H2O2 acts as both reducing agent.

Step-by-step explanation

Both the reactions are redox reactions.

In a redox reaction, reduction and oxidation undergo simultaneously wherein one species get oxidized and the other gets reduced.

Decrease in oxidation number indicates reduction and

Increase in oxidation number indicates oxidation

Looking at the given set of reaction, and classify oxidizing and reducing agent, you should know the oxidation states of each element as:

 

1] In the given reaction:

4 CaSO3 ? 3 CaSO4 + CaS

The oxidation number of element in reactants are:

CaSO3

Ca = +2 [electro positive element]

O = -2 [electro negative element]

S = +4

 

The oxidation number of element in products are:

CaSO4 

Ca = +2 [electro positive element]

O = -2 [electro negative element]

S = +6

 

CaS

Ca = +2 [electro positive element]

S = -2

 

Thus, it can be confirmed that the reactant undergoes redox reaction wherein the

1. oxidation number of Sulfur increases from +4 in CaSO3 to +6 in CaSO4. This is oxidation reaction.
2. oxidation number of Sulfur decreases from +4 in CaSO3 to +2 in CaS. This is reduction reaction.

 

Therefore,

CaSO43 acts as both oxidizing and reducing agent.

 

2] In the given reaction below

2 KMnO4+ 3 H2O2 → 2 MnO2 + 2 KOH + 2 H2O + 3 O2

 

The oxidation number of element in reactants are:

KMnO4

K = +1 [electro positive element]

O = -2 [electro negative element]

Mn = +7

 

H2O2 

H = +1 [electro positive element]

O = -1 [electro negative element]

 

The oxidation number of element in products are:

MnO2 

O = -2 [electro negative element]

Mn = +4

 

KOH

K = +1 [electro positive element]

O = -2 [electro negative element]

H = +1

 

H2O

H = +1

O = -2 [electro negative element]

 

O2

O = 0 [elemental state has oxidation number = 0]

 

Thus, it can be confirmed that the reactant undergoes redox reaction wherein the

1. oxidation number of Mn decreases from +7 in KMnO4 to +4 in MnO2. This is reduction reaction.
2. oxidation number of Oxygen increases from -1 in H2O2 to 0 in O2. This is oxidation reaction.

 

Therefore,

KMnO4 acts as both oxidizing agent.

H2O2 acts as both reducing agent.