Question

Consider the reaction between hydrogen peroxide and iron in acidic solution:
H2O2 (aq)+ F e^2+ (aq) + H2O (l)

1. Balance the reaction in acidic solution.
2. Determine the standard potential for this reaction.
3. Determine the potential for this reaction if the concentrations of hydrogen peroxide,
iron (II), and iron (III) are all 0.10 M and the solution is pH = 4

Answer 1

H2O2 (aq)+ F e^2+ (aq) -------> Fe+3 + H2O (l)

OXidation Half :

Fe+2 ----> Fe+3 + e-

Reduction half :

H2O2(aq)====>H2O(l)

Add water to the right to balance O

H2O2(aq)====>2H2O(l)

Add H+ to the left to balance H

H2O2(aq) + 2H+(aq)====>2H2O(l)

add e- to the left to balance charge

H2O2(aq) + 2H+(aq) + 2e-====>2H2O(l)

half reactions are

Fe^2+(aq)====>Fe^3+(aq) + e-

H2O2(aq) + 2H+(aq) + 2e-====>2H2O(l)

multiply the first one by 2 to get rid of the e- then combine the two equations

2Fe^2+(aq) + H2O2(aq) + 2H+(aq)====>2Fe^3+(aq) + 2H2O(l)

Now the equations is balanced.

Answer is:

2Fe^2+(aq) + H2O2(aq) + 2H+(aq)====>2Fe^3+(aq) + 2H2O(l)

2]

Eo = E oxidation + E reduction = 1.77 + 0.771 = 2.541 V

3]

Ecell = Eo - 0.0591/n * log Q

Q = [Fe+3]^2 / [H+2]^2 [H2O2] [ Fe+2]^2

Q = 10^9

n = 2 moles of electrons are transferred

Ecell = 2.541 - 0.0591 / 2* log 10^9

Ecell = 2.275 V