[FreeTheBee]

I think these last posts are actually quite relevant to your question. Although it seems to go a little off-topic the central issue is still, whether or not Fe(II) will be formed in acidic solutions.

One way to look at your question is based on pourbaix diagrams, the wikipedia page on this shows an example of the iron system. It shows that without complexing agents Fe(II) is stable in acid under 'regular' conditions, but as Borek already pointed out, the presence of oxygen can interfere, since it will lead to a more oxidising environment.

http://en.wikipedia.org/wiki/Pourbaix_diagram

You can also stabilise oxidation states using complexing agents, compare for example Fe(III)/Fe(II) (0.771V) to [Fe(CN₆)]^3-/[Fe(CN₆)]^4- (0.358V). In this case you're not dealing with just 'aquated' iron ions anymore though, but with complexes.

[FreeTheBee]

Where this idea of reversed potential comes from?

I should really quit leaving out bits and pieces :-) I know redox potentials as such do not change sign, but signs do come in when taking the difference between two half reactions to get the potential of a total reaction. In this case I implicitly subtracted the reduction of Fe(II) and Fe(III) from the reduction of protons under standard conditions (0V).

[Borek]

Note how Pourbaix diagram - again - contradicts the idea of Fe -> Fe³⁺ oxidation by H⁺ below 0 V.

[aeacfm]

i can see that you Forgot heart of the matter and every body want to prove some thing to him self

FeCl₂ solution acidified with HCl will not miraculously convert itself to FeCl₃ solution. Also dissolving ferrous salt in HCl will not lead to its oxidation, you will be still left with Fe²⁺.

lets make some thing prctical here
Only seconds ago , i dissolved Ferrous sulfate in concentrated HCl and take a portion of the solution and add KI solution IMMEDIATELY ?brown colour of iodine formed and adding chloroform the violet color of iodine appear in the oraganic layer of chloroform that shows that Fe⁺⁺⁺ NOT Fe⁺⁺ present in the solution may Fe++ present but traces  

[aeacfm]

when adding the DILUTED HCl (1:1) it takes more time to appear the iodine color than what happened with the CONCENTRATED HCl

[Borek]

Ferrous sulfate or Mohr salt (Ammonium iron(II) sulfate)? Most ferrorus salts are unstable and get oxidized by the air oxygen, so they are always contaminated by Fe(III). Mohr salt is relatively stable.

Note that your solution is all the time in contact with air and it is saturated with oxygen, so small amounts of iron(II) will be oxidizied immediately. Check if using freshly boiled water (and perhaps a boiled acid) won't slow the oxidation further down.

Just because iodine forms doesn't mean your solution contains only Fe³⁺. Most likely you have some mixture of Fe(II)/Fe(III). If you want to be sure it is only Fe(II) you need to reduce it down, that's a standard procedure before determination of Fe(II) by any redox titration.

[aeacfm]

If you want to be sure it is only Fe(II) you need to reduce it down, that's a standard procedure before determination of Fe(II) by any redox titration.

thats exactly what i need
how can i achieve this standard ?in other words how can i be sure that the iron II will not oxidized when i want to identify the iron III in mu sample ?

simply thats what i want 

[Borek]

Determine Fe(II), reduce all, determine sum.

[aeacfm]

Determine Fe(II), reduce all, determine sum.

thats better but lack of chemicals and time are disadvantages

then correct me if iam wrong
i make mix of hydroxyle amine +HCl (1:1) the mix was 1:1 and do the previous iodine test with ferrous sulfate  and the test was -ve so do what i performed accepted practically