Question

What is redox reaction? Identify the substance oxidized and the substance reduced in the following reaction.

i) 2PbO + C → 2Pb + CO2
ii) CuO + H2 → Cu + H2O
iii) 4Na + O2 → 2Na2O​

Answer 1

Answer:

Sodium atom to sodium ion: oxidation, e loss, ox. state change is from 0 to +1

2 x Na increases, each from (0) to (+1), losing one electron per Na atom, which is 'electronically' balanced by the oxygen molecule to peroxide ion: reduction, e gain, ox. state change 2 x O decreases, each from (0) to (1), gaining two electrons per O atom (or two electrons per O

2

molecule), and the halfreactions are:

(i) oxidation: Na → Na

+

+ $$e^$$ (formation of sodium ion)

(ii) reduction: O

2

+ $$2e^$$ → O

2

−−

(formation of the peroxide ion)

Adding and balancing 2 x (i) + (ii) gives the full equation

4Na (s) + O

2

(g) → 2Na

2

O(s)

Sodium (Na) is oxidised as it gains oxygen and oxygen gets reduced.

Option A is correct