I just went though a reaction wherein hydrogen gas is liberated and hence restricts the product formed to ferrous and not ferric salt. I just want to know how H2 gas gets its reducing property? It has a moderate bond strength also if I am not wrong.

  • $\begingroup$ "Liberation of hydrogen prevents the formation of ferric chloride." $\endgroup$ – JM97 Sep 16 '16 at 13:09
  • $\begingroup$ When HCl reacts with Fe it is H+ which gets reduces and not H2 gas. $\endgroup$ – JM97 Sep 16 '16 at 13:15
  • $\begingroup$ H+ reduces or gets reduced to H2? $\endgroup$ – Hani Sep 16 '16 at 13:34
  • $\begingroup$ H+ gets reduced to H2. Also the first comment is my textbook statement please see my views in my answer. $\endgroup$ – JM97 Sep 16 '16 at 13:40
  • $\begingroup$ H+ gets reduced to H2. OK. But how can H2 in its gaseous state, reduce Fe+3? $\endgroup$ – Hani Sep 16 '16 at 13:45

Iron on reaction with HCl forms Fe(II) salts and not Fe(III) salts because even if Fe(+3) is formed, as we can see in electrochemical series Fe(+2) will be favoured ie. H2 which gets can reduce Fe(+3) to Fe(+2). So thermodynamically Fe(+2) salt is favoured. If you want to make Fe(+3) salt then you can react Fe and Cl2 directly.

How H2 gets its reducing property?

H2 gas will react with FeCl3 to form FeCl2 and HCl. I don't know the exact mechanism but it can be explained well on the basis thermodynamic data available.

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  • $\begingroup$ I agree with the answer. Just thought to say this- 'not in every condition though. At some conditions,may be the reverse reaction would be favoured(by Nernst equation)' $\endgroup$ – Amritansh Singhal Sep 16 '16 at 13:46
  • $\begingroup$ @AmritanshSinghal but the reaction is carried in a closed inert atmosphere of N2 so H2 evolved will not get liberated and react with Fe(+3). $\endgroup$ – JM97 Sep 16 '16 at 14:06
  • $\begingroup$ I guess you are correct. $\endgroup$ – Amritansh Singhal Sep 16 '16 at 14:08
  • $\begingroup$ @AmritanshSinghal inert atmosphere is required to prevent O2. $\endgroup$ – JM97 Sep 16 '16 at 14:12

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