Respuesta :
In the reaction, S₄O₆²⁻(aq) + 2I⁻(aq) → I₂(s) + S₂O₃²⁻(aq) the oxidising agent is I₂(s) and reducing agent is S₄O₆²⁻(aq).
What is Oxidation?
Oxidation is said to take place when:
a) oxygen atom is added to the substance
b) hydrogen atom is removed from the substance
c) electron is removed from the substance
As a result there is an increase in oxidation number of central atom.
What is Reduction?
Reduction is said to take place when:
a) oxygen atom is removed from the substance
b) hydrogen atom is added to the substance
c) electron is added to the substance
As a result there is a decrease in oxidation number of central atom.
What is oxidising agent?
An oxidising agent is a substance that is capable of oxidising other substances and itself undergoes reduction i.e. decrease in oxidation number of central atom.
What is reducing agent?
A reducing agent is a substance that is capable of reducing other substances and itself undergoes oxidation i.e. increase in oxidation number of central atom.
Given,
S₄O₆²⁻(aq) + 2I⁻(aq) → I₂(s) + S₂O₃²⁻(aq) ΔG° = 87.8kJ/mol
As the sign of change in Gibbs Free Energy is positive, in the given equation, the forward reaction is non-spontaneous and backward reaction is spontaneous.
Thus the equation is re-written as
I₂(s) + S₂O₃²⁻(aq) → S₄O₆²⁻(aq) + 2I⁻(aq) ΔG° = -87.8kJ/mol
In the above equation,
The oxidation number Iodine in I₂(s) is 0 and that in 2I⁻(aq) is -1. There is a decrease in oxidation number from 0 to -1 and thus I₂(s) is oxidising agent.
The oxidation number of Sulphur in S₂O₃²⁻(aq) is +4 and that in S₄O₆²⁻ is +6. There is an increase in oxidation number from +4 to +6 and thus S₂O₃²⁻(aq) is reducing agent.
Thus in the given reaction, I₂(s) is oxidising agent and S₂O₃²⁻(aq) is reducing agent.
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