Question

Indicate which reactions are redox reactions. check all that apply. check all that apply. 2na(s)+cl2(g)→2nacl(s) cd(s)+pb2+(aq)→cd2+(aq)+pb(s) pb(no3)2(aq)+2licl(aq)→pbcl2(s)+2lino3(aq) c(s)+o2(g)→co2(g)

Answer 1

Redox reactions are those in which the oxidation numbers of the elements involved are changed.

Equation 1:

2Na(s) + Cl2(g) --> 2NaCl

 

The oxidation numbers of Na and Cl in the reactant side are both zero because they are in elemental form. In the product side, however, the oxidation numbers are +1 and -1, respectively. Hence, this is an example of redox reaction.

Equation 2:

Cd(s) + Pb+2(aq) --> Cd2+(aq) + Pb(s)

The oxidation numbers of Cd and Pb+2 in the reactant side are 0 and +2, respectively. They are, however, +2 and 0 in the product side. Hence, this is also a redox reaction.

Equation 3:

Pb(NO3)2(liq) + 2LiCl(aq) --> PbCl2(s) + 2LiNO3(aq)

The oxidation numbers of the involved ions (both cations and anions) are not changed. Hence, this is NOT an oxidation reaction.

Equation 4:

C(s) + O2(g) --> CO2(g)

 Just as the equation 1 and 2, the oxidation numbers of the reactants are not similar to those in the product. Hence, this is an example of oxidation reaction.