Question

justify giving reaction that among halogens fluorine is the best oxidant and among hydrohalic compound, hydroiodic acid is the best reductant?

Answer 1

Among the halogens best oxidant is F2 and oxidizing character decrease in the order F2 > Cl2 > Br2 > I2

Since F2 + 2e- → 2F- (aq) . Ered0 + 2.87

is maximum among the halogens so much so that F2 can displace.

Cl-, Br- I- from their salt solution to Cl2.Br2, I2 respectively.

F2 + 2NaCl(aq) → 2NaF (aq) + Cl2

F2 + 2NaBr (aq) → 2NaF + Br2

F2 + 2NaI(aq) → 2NaF + I2

Cl2 + 2NaF → No reaction

i.e. F2 can be reduced most readily.

Hence, F2 is the stronger oxidizing agent.

But among the hydrohalic acid HI is the strongest reducing agent.

The reducing power of halogen acids depends upon the ease with which they decompose to give H2 & X2. This in turn depends upon the bond dissociation energy. Since the bond dissociation energy of the halogen acid increase in the order.

HI < HBr < HCl < HF

Therefore reducing power of these acids increase in the reverse direction.

HF < HCl < HBr < HI