pl.........help required in chemisrty........?

it sounds like you want an electrolyic cell, where DC voltage is applied,

as opposed to a galvanic cell, which is a spontaneous redox...

if not email me from my avatar

(for Fe2+ will not spontaneously react with H+ as a galvanic cell)

http://bilbo.chm.uri.edu/CHM112/tables/redpottable...

reduction: 2 H+(aq) + 2 e– ---> H2(g) Eo = 0.00

reduction: Fe2+(aq) + 2 e– ---> Fe(s) Eo = –0.440

your reduction, that requires lower voltage, will be

2 H+(aq) + 2 e– ---> H2(g) Eo = 0.00

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as for the oxidation:

reduction: Fe3+(aq) + e– ----> Fe2+(aq) Eo = 0.771

reduction: O2(g) + 4 H+ (aq) + 4 e– ---> 2 H2O(l) Eo = 1.229

gives oxidations as:

oxidation: Fe2+(aq) ---> Fe3+(aq) + e- Eo = - 0.771

oxidation: 2 H2O(l) --> O2(g) + 4 H+ (aq) + 4 e– Eo = - 1.229

your oxidatioon that has the lower voltage requirement is:

Fe2+(aq) ---> Fe3+(aq) + e- Eo = - 0.771

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your electrolytic cell would be

oxidation: Fe2+(aq) ---> Fe3+(aq) + e- Eo = - 0.771

reduction: 2 H+(aq) + 2 e– ---> H2(g) Eo = 0.00

your products would be Fe+3 & H2

p.s.

http://docs.google.com/viewer?a=v&q=cache:6-RHfQBA...

Pt|Fe2+(aq)|Fe3+(aq)||H+(aq)|H2(g)|Pt(s) Ecellº = -0.77 V