Question 16.
Identify from the following reactions the reactants that undergo oxidation and reduction.
a. Fe + S → FeS
b. 2Ag2O → 4 Ag + O2
c. 2Mg + O2→ 2MgO
d. NiO + H2→ Ni + H2O
Answer:
a. Fe + S → FeS
In the given reaction, Fe is giving 2 electrons to Sulphur. Sulphur is accepting those electrons. This means:
⇒ Fe undergoes oxidation (to lose electrons)
⇒ Sulphur undergoes reduction (to accept electrons)
b. 2Ag2O → 4 Ag + O2
⇒ Ag in Ag2O has oxidation state= +1
Ag in Ag(s) has oxidation state = 0
This means Ag undergoes reduction
⇒ O in Ag2O has oxidation state = -2
O in O2 has oxidation state = 0
This means oxygen undergoes oxidation
c. 2Mg + O2→ 2MgO
First write the half reactions:
Mg0 → Mg2+ + 2e-
O2 + 4e-→ O2-
⇒ Oxygen goes from 0 to -2. Thus, it undergoes reduction.
⇒ Magnesium goes from 0 to +2. Thus, it undergoes oxidation
d. NiO + H2→ Ni + H2O
First write the half reactions:
2H0 - 2e-→ 2H1
Ni2+ + 2e-→ Ni0
⇒ Hydrogen goes from 0 to 1. Thus, it undergoes oxidation.
⇒ Nickel goes from 2 to 0. Thus, it undergoes reduction.
