Question

Only for the redox reactions below, state which substance was oxidized, which substance was reduced, and the total number of electrons involved.

a) SO3(aq) + H2O(l) -->H2SO4(aq)

b) Zn(s) + CuCl2(aq) --> ZnCl2(aq) + Cu(s)

c) 2 CO(g) + O2(g) --> 2 CO2(g)

*A is not a redox reaction*

Answer 1

Whenever there is an increase in oxidation number, it is called as oxidation and reduction in oxidation number is called as reduction. Each change in oxidation number is caused by addition or removal of electron.

As A is not redox reaction lets see B and C

In B , Zn has oxidation number of 0 in reactant and +2 in product so it has got oxidised, by removal of 2 electrons.

Copper has +2 oxidation number in reactant side and 0 in product, so it got reduced by addition of 2 electrons.

There is no change in oxidation number of chlorine, so neither oxidised nor reduced.

In equation C , carbon has +2 oxidation number in reactant, and +4 in product so it got oxidised by removal of 2 electrons.

Oxygen has 0 oxidation number in reactant and -2 in product so it got reduced by addition of electrons.