Which acts as an oxidant and which act as a reductant.a. 2Cu2O(s) + Cu2S(s) → 6Cu(s) + SO2(g)

Question

Justify that the following reactions are redox reaction; identify the species oxidized/reduced, which acts as an oxidant and which act as a reductant.

a. 2Cu₂O_(s) + Cu₂S_(s) → 6Cu_(s) + SO_2(g)

b. HF_(aq) + OH^-_(aq)  → H₂O_(I) + F^-_(aq)

c. I_2(aq)  + 2 S₂O₃^2-(aq) → S₄O₆^2-_(aq) + 2I^-_(aq)

Answer 1

i. 2Cu₂O_(s) + Cu₂S_(s) → 6Cu_(s) + SO_2(g)

a. Write oxidation number of all the atoms of reactants and products.

b. Identify the species that undergoes change in oxidation number.

c. The oxidation number of S increases from -2 to +4 and that of Cu decreases from +1 to 0. 

Because oxidation number of one species increases and that of the other decreases, the reaction is a redox reaction.

d. The oxidation number of S increases by loss of electrons and therefore, S is a reducing agent and it itself is oxidised. 

On the other hand, the oxidation number of Cu decreases by gain of electrons and therefore, Cu is an oxidising agent and itself is reduced.

Result :

1. The given reaction is a redox reaction. 

2. Oxidant/oxidising agents (Reduced species) : Cu₂O/ Cu₂S 

3. Reductant/reducing agent (Oxidised species) : Cu₂S

[Note : Cu in both Cu₂O and Cu₂S undergoes reduction. Hence, both Cu₂O and Cu₂S can be termed as oxidising agents in the given reaction.]

ii. HF_(aq) + OH^-_(aq)  → H₂O_(I) + F^-_(aq)

a. Write oxidation number of all the atoms of reactants and products.

b. Since, the oxidation numbers of all the species remain same, this is NOT a redox reaction.

Result :

The given reaction is NOT a redox reaction.

iii. I_2(aq)  + 2 S₂O₃^2-(aq) → S₄O₆^2-_(aq) + 2I^-_(aq)

a. Write oxidation number of all the atoms of reactants and products.

b. Identify the species that undergoes change in oxidation number.

c. The oxidation number of S increases from +2 to +2.5 and that of I decreases from 0 to -1. 

Because oxidation number of one species increases and that of the other decreases, the reaction is a redox reaction.

d. The oxidation number of S increases by loss of electrons and therefore, S is a reducing agent and itself is oxidised. 

On the other hand, the oxidation number of I₂ decreases by gain of electrons and therefore, I is an oxidising agent and itself is reduced.

Result :

1. The given reaction is a redox reaction. 

2. Oxidant/oxidising agent (Reduced species) : I₂ 

3. Reductant/reducing agent (Oxidised species) : S₂O₃^2-